Villager spawn eggs never spawn nitwit villagers

The Bug:

Villager spawn eggs never spawn nitwit villagers.

Steps to Reproduce:

1. Spawn multiple villagers by using spawn eggs.
2. Take note as to whether or not villager spawn eggs occasionally spawn nitwit villagers.

Observed Behavior:

Villager spawn eggs never spawn nitwit villagers.

Expected Behavior:

Villager spawn eggs would occasionally spawn nitwit villagers.