If you set out to build "the one big marketplace", you inevitably get to a place where mostly what your marketplace offers is crap, because you have optimized it towards providers putting stuff onto your marketplace.
Thus, in building "the big marketplace", you necessarily fail to optimize it towards users getting value out of the marketplace, because you kinda sorta hoped that would be taken care of by "free market" pressures. (And also because it's one of those "hard problems" that you would rather forget about and build some neat code instead.) But it's the users bearing the collateral damage.
I'm currently working on a package/application distribution system that is decentralized and the "app-pocalypse" is one of the reasons why I made it so. Being decentralized means that the value you are getting out of it depends mainly on the trust you invest in your immediate channel provider who in turn now has a responsibility to keep you happy. By splitting up the relationship and giving people proper roles instead of the delusion of a grand audience that is fit for whatever some app developers shovel into the system, I hope it will end up providing actual value instead of just a top-down revenue system.
Having worked on it for a while now, it always strikes me as weird how we are all on the Internet (which by its design is fault tolerant and decentralized), building these centralized, monolithic services that inevitably fail (either in a big way due to security reasons or in a slow way, like in the app-pocalypse) for the same reasons.