I think a big reason we’ve seen some apps struggle to keep up development for elementary OS is that distribution was a pain. Using Launchpad, creating automatic builds in a PPA, creating some sort of website/landing page, and giving users Terminal commands to add the app just was not a good experience or easy to do for a lot of people. Not to mention the security implications of users adding random PPAs for each app they want to use.
Even with that, there are already several dozen known apps being made for elementary OS specifically.
The existing pains of distribution are a huge reason behind AppCenter and its whole design: we’re moving to where the developers already are (GitHub) and providing a crazy easy way to get those apps built and distributed to users (AppCenter). We’re also making discovery as easy as possible: apps are featured right in the store on the user’s desktop. Plus, it’s now very easy for developers targeting elementary OS to get paid for their apps.
AppCenter gives developers a clear, easy path to distribution and promotion to users while enabling them to get paid for their work. It’s a pretty awesome setup and we’re excited to continue expanding our beta testing and release it to the public soon. :)