>>529308219
I've often said that Hoyo realized that investing more money in a single gacha did not return more money so they branched out and starting making more games of the same budget, thus discovering the best return per dollar of budget.
But now that you mention it, the next step after branching out to different games, may be beginning planned obsolescence since gachas experience by far more profit during their launch. It's hard to say if this big boost at initial launch is enough to cover the set-up cost though, since these games are meant to be recurring revenue sources.
Also, Acheron's banner was, by pull tracking aggregates, more profitable than Seele's launch banner so HSR may have been more profitable in year 2 than year 1 which could turn things on it's head. ZZZ and Genshin have only ever decreased in popularity however, at least to my knowledge. Since the pull trackers were not invented yet during Genshin's launch it's difficult to gauge the success of Raiden's banner to Venti's.
