C2 has not even been out as long as many popular large-scale indie games have been in development, so there's that. Also there were a number of great games being made in C2 that were ultimately canceled or switched to other engines due to breaking changes and frustration with C2's reliance on 3rd party technologies.
There are a number of great and popular CC/C2 titles, but the front page shows very few. It's pretty amazing that games like The Iconoclasts aren't on there. A better/dedicated showcase page would be nice, but I'm sure it will take a lot of time for Scirra to evaluate projects and decide what should and shouldn't be on there...valuable time that could be spend working on C3 and more important things.
Its gotten super easy to make games (despite idiotic complaints about third party issues), and the market is super saturated.
So to sell anything you have to spam the world, which is basically what Supercell, does.
That or hit on some viral game mechanic( Flappy Bird, Agar.io, Slither.io)
Not necessarily. Good games market themselves. If you can manage to get a single article on a site like Destructoid, where dozens of other gaming news outlets rip their content from, then you're pretty much set. Also, the complaints about third party issues are totally legitimate. Just ~6 months ago NWjs started throwing JS errors, many features like window scaling and audio broke, the debugger didn't work, we all got ghost processes, and so on. And that was after at least a year of dealing with that whole "jitters janks and snags" issue. And that's just NWjs. I can't even begin to list the problems with all the mobile shit.