End biomes in "Single biome" selection resort to default overworld

What I expected to happen was...:
It would come up with the ender biomes, like in past versions.

What actually happened was...:
It would default to the overworld with end structures.

Steps to Reproduce:
1. Open 1.20.1
2. Create world
3. Select "Single Biome"

4. Select any end biome