Yeah that makes sense. But why are most games sold on steam? They are all digital contents that could be sold on the web right?
But to live the very point of the discussion, may be it's the target group.
With games, the target group are gamers. It's a closed group. You can say, games are developed just for that group and having a place for just that group is a push of selling point. So, pretty easy to do.
With general software, the market isn't so easy to cluster. You can have a market selling office software. What about the tools, server and special needs software? Actually, you need a market for each subdivision, for the customers to be able to find what they looking for in that specific cluster of needs.
its just the mass and different solutions for the same problems.
We have software catalogues, we have other sources of information what software might be most of use for us. We have open source libraries, where you too can search for specific softwares. And then, we have "Standard" softwares that are used mostly in their special field of application (e.g. Photoshop).
I don't see a way to make a Universal "app store". As a developer, i wouldn't take part in that, as I have other ways of distribution. May be some better fitting ones for my target group