The Bug

Possibly related to MC-279714

As of 25w02a, farm animals were made to be able to spawn in all Badlands biomes. Despite this, in practice, they only spawn in Wooded Badlands, as they're only able to spawn on grass still.

This change may seem innocent, but I assume that as a result of this, in the normal Badlands biomes where only armadillos are actually able to spawn since they can spawn on terracotta, Armadillos spawn much less despite nothing else taking up their space.

This makes Badlands biomes feel extremely empty again, which was something the Armadillo had previously addressed.

Example Screenshots

Seed: -5853161135001706410
Coords: 596, 1211515

In 1.21.5:

In 25w02a:    

In some other seeds, sometimes you'll have a large Badland area with only 2 or 4 Armadillos around total, which is a DRAMATIC dropoff from the many you'd see before.

Conclusion

In the superflat worlds, you can more clearly see the spawning difference. With only 1 armadillo present while other farm animals spawn, compared to previously large groups of armadillos spawning. This is however, true even in normal worlds with average Badlands where the farm animals don't actually seem to spawn outside of sparsely doing so in wooded badlands, as per MC-279714

Farm animals eat up their spawning weight despite not actually being present 90% of the time