I think this is a bug, but maybe it was "works as intended"

What I expected to happen was...:
Wandering Traders that are named using the name tag never despawn in the world.

What actually happened was...:
We can't make Wandering Traders never despawn whithout cheat! (Such as using spawn eggs or use /summon commmand.)

Steps to Reproduce:
1. Find a Wandering Trader that spawned in nature.
2. Using name tag to named it.
3. Wait for 40 minutes, it would disappeared!

I can't use English very well, so this description maybe had some grammars are wrong.