Why BOT ratings never surpass 3000 ?

Here in Lichess the highest human rating is always higher than the highest BOT rating. Why ?

Yes some bots got past 3000 bullet, but it seems like they could not keep it.

One may state that bots don't have enough pool of players at this level, based on the fact that top GMs don't waste their time playing rated against bots. That's a fact.

However, they can get from lower rated bots, which get from lower rated bots, until some level like 2400 bot which actually gets to play rated against some humans, sometimes. And shouldn't that mean that humans and BOTS play in the same pool?