"Glass Bottom Games" made me start this topic, but it is a reoccurring theme.

Case 1: Hot Tin Roof
Although it is sold on Steam and GOG, the official page does not only advertise Steam exclusively, it also links direktly to the "buy" button there while GOG isn't even mentioned.

Case 2: Skatebird
The released a demo on itch.io to gather more funds via Kickstarter that is now taken offline since they apparently have enough funds and even on the now modified itch.io page there is no mention of a release of the full game there and the official site yet again only points to buying it on Steam, effectively abusing itch to gather funds to sell it elsewhere.

Now those are just two examples, but since there are some lawyers around here, could someone tell me whether such things aren't violating some anti-monopoly laws or something related?

And now to Epic...
Many studios have gathered funds to release a game on Steam/Linux/etc.... only to then switch to Epic (and therefore automatically also Windows) exclusivity even if the game was already successfully funded.
Where's the legal line you can't cross? Is there one at all in corporatocracy?

Also feel free to discuss and especially add more examples.

Also what about prices often being inflated on GOG for fewer features than on the sometimes cheaper Steam?
Isn't that against fair competition?

In both cases, it appears that it is the developer or publisher who decided to go to Steam. That developer or publisher isn't a monopoly, so antitrust laws don't apply. Now if Steam somehow abused their market dominance to effectively force the publisher to release on Steam only, there'd be a problem. Unfortunately the laws and actual actions taken with respect to monopolies are fuzzy as fuck so it's very difficult to establish 1) whether steam is a monopoly 2) whether anything steam does to encourage publishers to use their platform is abuse of market dominance. There's no line, corps can break promises as much as they like, especially when it comes to dirt cheap consumer products. If someone has a beef with them, they just settle it by offering a refund. Random Joes don't have the money and drive to take it to court (and they have very little leverage when they can't show that not getting a Linux version of a game caused massive damage as measured in $$$), so the calculated risk of breaking promises is close to nil. It's just another expense on the sheet if it comes to that. Advertising today is just full of lies and there's no oversight.

With my limited knowledge, I'd like to say that a quick google search shows no precedent regarding delivering on features promised during crowdfunding campaigns. In the absence of law relating to crowdfunding in all countries as far as I know,there is nothing but the word of the people running the campaign to bind them to what they say. There is no contract between the parties in a crowdfunding campaign and the current trend online seems to lean more towards viewing it as an investment (in which there is a risk element) rather than a commercial transaction for defined goods / services; see Fig for example.

Many countries are so through and through corrupt and the corporations (aka mafia groups) can do almost whatever as long as no lawyers see money in suing them.