It must work on the phone people actually own
The benchmark device is not a flagship. It is a two-year-old budget Android with 2 GB of RAM and a screen that has seen better days. If a slot title stutters there, it does not go into the lobby until the studio optimises it — regardless of how well it performs on test hardware in a studio office.
This is also why the library is curated rather than enormous. Every additional title is another thing to test, and a lobby full of games that half-work is worse than a smaller lobby where everything runs.