Summary
Any zombies (normal, villager, husks, drowned) can pick up glow ink sacs, which can cause to reduce and clog up the mob spawn rate in the caves since they don't despawn when holding any items in their hand. This was changed on Java 1.17.1-pre1 to solve this issue, and this bug report can be considered a parity issue.

Step to Reproduce
1. Set to hard difficulty, night time, and let mob spawn.
2. Throw glow ink sacs to the zombies.
3. Go far away around 100+ blocks, and then come back to the said zombie.
---> They don't despawn.