One of the biggest hurdles of playing old games is simply getting them to run and the major reason for this is obviously the changes in hardware and operating system software, which is not compatible with many old programs.
GOG does a fine job of getting these old games to run but, with so many of them, I can imagine that it sometimes gets challenging.

An obvious solution is to release emulators for old operating systems, similar to DosBox. I am sure that everyone would jump at the chance of getting their hands on such emulators even if you have to buy them.

My question is why hasn't Microsoft or any other taken this opportunity? They certainly stand to make money from such a venture, even if the emulator is sold cheaply. What are the legal and other blocks that are preventing us from getting these emulators?

Just as effort is given to retain and maintain old music and movies, I believe video games should be given the same courtesy. This is one of the many reasons why I support GOG's efforts.

Microsoft can make more money from you buying new Windows and other programs from them. Even if I also think they could make selling emulators profitable in itself, I suspect they fear cannibalising their sales of newer programs.

Windows does include some backwards compatibility, compatibility mode for instance. Of course with the thousands of different builds, drivers, and such like it's quite difficult to emulate everything. Hence why you have virtualisation and emulation. Also, even if there was a perfect layer, there would be things like securom which was specifically removed from windows 10 support, they wouldn't want to say not use and still provide it. Afraid I don't ever see a one size fits all, it's just not in anyone's interest other than the enthusiast.

Oh, now my brain popped up a couple of names: ScummVM and dgVoodoo.

Yes I think that probably is their philosophy, but I think by now there is a fairly large market for old programs, specifically video games, as evidenced by GOG.
If OS creators could allow sites like GOG to release an emulator with each game separately, similar to how it is done with DosBox, then that should ensure that old games remain playable without the OS emulator impacting other programs.

An emulator with every game, so xxmb extra per game, not mention all the maintenance, releasing new versions of every game when the emulator s updated etc. It's far too much work. Far simpler to provide the game and users can choose which type of emulation to use, some might like older emu some might like a modern engine replacement. It's just not practical or profitable.

If Microsoft perceived this as being a highly profitable venture worth their time and engineering resources, they'd most likely already be selling such a product.

In reality, the best way to handle old operating systems is either on old original hardware from the era of the operating system, and the market for people producing new hardware etc. to do that is extremely niche and likely close to nil, as well as being fulfilled by already existing used or old stock hardware for sale on eBay, Craigslist, etc. The volume of such sales is likely so small to not even be remotely on the radar of any major corporation like Microsoft, although it might be doable for some Mom and Pop niche enthusiast Amazon/Ebay storefront, although I doubt it'd make much profit more than pocket lint.

On the software side of things the most viable way to go is using virtual machines, and that works well for a lot of applications including old games, but it has some limitations as well, in particular with handling 3D acceleration. VMware probably has the best support for that out there, however VirtualBox supports it as well (although that is very unreliable in my personal experience). The ideal solution would be to see the virtual machine software companies improve support for 3D acceleration thunking, and adding additional emulation/simulation for certain other hardware specific to gaming. While that is technically possible, it is very highly unlikely for them to actually bother doing it because in the case of the software that is developed for profit, they spend their engineering resources (money, manpower) developing technologies that bring in the maximum amount of money. That more or less means stuff for big business, data center servers, virtual hosting, etc.

Adding features specific to making video games run and reallocating engineering resources to doing that would have to be seen as something that they themselves predict would drive up revenue more than spending those resources on improving features for their existing big-buck customers in data centers and cloud computing. Unfortunately for gaming, the number of people who would purchase their products and for what price they'd be willing to pay to have such features is most likely an extremely small niche group of people that would generate so little revenue as to not be worth spending the time to bother doing it.

The same answer I think is true for a company like Microsoft to put out a product to run old games. "There's no money in doing it." or "There is no viable business market for it." does not mean that there are zero people out there who would pay for it, but rather it means that the total number of people out there who would pay for such a product is so small that there is no viable business justification to draw resources away from other development products that are known profit makers for existing known profitable markets.

If people want to see such things, about the only way I can see them ever happening is in a development model that is not profit driven, which more or less means an open source project that is volunteer driven. VirtualBox is open source, so if there are enough gamers out there who care about such things, they might want to get involved with improving 3D support in VirtualBox as that's probably the best actual solution that is viable for this sort of thing and actually does exist already, just not quite in a reliable state for this usage case.

I run many old games and don't have any problems. But can I just say one of the things I am doing is running Windows XP SP3, in a VirtualBox. You could also do this if you are having problems... or you could Dual-Boot XP. The reason why I recommend XP is this:
You can run a modern OS: Vista/7/8/10, and it will run modern games and hopefully most older ones.
Virtual/Dual-Boot an old os: Preferably XP, and it will run XP, ME, 2000, 98, 95 games.
DOSBox in your modern OS: For the DOS games.

Now your PC is complete for all games!