"However, at night, drowned swim to the surface and chase players as well as baby turtles, even outside the water, like regular zombies." – Minecraft Wiki

Drowned are intended to have the ability to emerge from the water specifically at night. This does not work consistently in the current version (1.17.1), in 1.16.5, or in 1.15.2.

Curiously, this remains inconsistent. When testing on Superflat worlds in all three versions, the Drowned never emerge. In version 1.15.2 on Default world generation, the Drowned did emerge and follow the player.