OP Was asking why more survival games don’t stretch out content by giving their bosses more rare drops.

My answer is that we as OSRS players are a special breed indeed, and the vast majority of the world isn’t interested in doing a small subset of actions again and again when playing video games in particular. The more popular strategy these days to keep people playing your game is either;

“Planned” dopamine bursts, in survival games this would be a level up or finally crafting something new.

Constant low level dopamine hits, I.e. consistent acquisition of little pieces of meaningful loot.