Oh please.
They just don't care.
Take Steam for instance, I have a thousand times better experience finding new games on there than I have on any mobile app store. I get recommendations from my friends, according to what Steam thinks I would enjoy playing, and they even have curators for apps so people whose reviews I can enjoy can list games with a short review. And those are just a few ways of discovering new games, there are a ton of others.
Neither Apple nor Google are even trying. That's the problem. They don't give a shit.
Valve barely gives a shit about improving Steam — since it'll print more money than they can ever spend regardless — and still they've surpassed both Google and Apple.