What Will Happen When Miners Stop?

I have been wondering, if miners are keeping the bitcoin network safe and up. They do it to mine bitcoin. Once no any bitcoin left to mine, why would miners continue to keep network up and safe?

I know this is not a topic for many decades but lets assume we are at 2150 there is no any bitcoin left to mine + no halving left why would miners continue?

Lets assume for fees, this means we expect bitcoin to be more adopted and have more transactions. Lets say it didn’t get adopted as expected and still there are not millions of transactions. May it lead miners to shut down since its not profitable, then may it lead bitcoin network being vulnerable to 51% attack?