Too many pillagers spawn around pillager outposts in Superflat worlds of Overworld preset

Steps to reproduce

1. Create a new world of Superflat type and Overworld preset.

   1. In the world creation screen, navigate to the World tab.

   2. Set the world type to Superflat.

   3. Click on the Customize button, then on the Presets button.

   4. Select the Overworld preset.

   5. Apply the changes and create the new world.

2. Locate a pillager outpost and teleport to it.

   1. Run the following command.

      locate structure minecraft:pillager_outpost

   2. In the chat window, click on the highlighted coordinates to copy them as a tp command, then run it.

3. Wait for pillagers to spawn.

Observed behavior

A large number of pillagers will be spawned at the outpost.

Expected behavior

Only a few pillagers would be spawned.