That's because 1) these titles were downloaded soooo many times before the insane competition of nowadays, and 2) these games are constantly being rewritten. The original executable of any old game won't run any more on the latest OSes. You are told as a developer 'IOS n is being deprecated. Rewrite your app or it'll be axed from the App Store.' I don't think the same forced upgrades happen on Android but you will get bugs and problems if you don't update. Certainly to use current features like Play Services you have to update your app, recompiling for the latest OS targets and APIs.
So Angry Birds in the top download spot is there because 50 million downloaded the original giving it a 50 million headstart and then 300 million have subsequently downloaded the rebuilt versions over the years, including all the original copies being updated such that the original game doesn't exist.
In truth the analogy would be every console dev reworking their game to run on the new machine - your download library would work on PS5 because the devs rebuilt it from source. Obviously that's not as economical as on mobile. On mobile, keeping your game up to date means having a new audience of hundreds of millions who haven't bought into it yet. On console, its more a case of the million who were going to buy your game did so already and that same audience now wants it rewritten to work on their new console, for free. You probably won't sell another million to new console gamers who hadn't bought it previously. The PS2 BC library on PS4 is extremely barren, I guess because these games don't make enough sales to justify the expense. The economy on consoles is actually better suited to selling remakes. It's in the hardware company's (not devs') best interests to maintain BC as that encourages users into the platform and ties them to the ecosystem.