The site seems geared towards purposefully making it hard to navigate to individual games of interest by leaving out features such as this, or detailed price filtering (where you punch in the price range yourself, not pre-determined ranges), or price sorting, etc. I think the general idea is if you can't easily sort and filter the game list the way that you'd like to in order to optimize your time and effort, that you then have to manually pore over much more of the catalogue, and they're hoping that you will find and buy games you wouldn't have if you could get to what you wanted right away.
That might actually increase sales with some users, but I know for me it causes me to buy less because I can't easily filter out what I don't want and filter in what I do want. As the store gets more and more games it becomes ever increasingly hard to filter out stuff I just do not want to see and will never buy.
The sad thing is that the amount of effort it takes to write a simple price sort and some simple filters should be a few days to a week at best, and that's giving them the benefit of doubt IMHO. It's not that they can't or wont do it, it's that it just isn't a priority for whatever reason.
They need to allocate their developer resources very carefully due to finite resources, so that they can work on things like removing the option to configure where your downloads get stored for example. Such features don't invent themselves afterall! :)
All seriousness aside though, and on a humorous note now... I wonder how much longer it will be until Adalia Fundamentals and Barefoot Essentials are comprised of more code than the GOG website is.
</it's a joke> :oP