Woodland mansions cannot be generated with the /place command in a superflat world.

I cannot generate woodland mansions with the /place structure mansion ~ ~ ~ command in a superflat world.Why can't you use commands to generate woodland mansions in a superflat world?

How to reproduce:

1. Create a superflat world.
2.  Input " /place structure mansion ~ ~ ~ "
3.  You can see the report.