Most hostile mobs aren't spawning even under the right conditions

Most hostile mobs no longer spawn even if their spawn conditions are met. Only mobs that spawn under special conditions(like Creakings, Wardens, and Drowneds with ocean ruins) spawn at all.

 

Steps to reproduce:

1-Create any world(a Superflat one showcases it best)

2-Set time to night

3-Notice how no hostile mobs spawn whatsoever

 

You can also immediately notice upon creating a Superflat word that the slimes that are usually everywhere don't spawn