Board Thread:General Discussion/@comment-1636709-20190513170353/@comment-4963061-20190519054323

When Ben 10 Alien Force came out, they "recycled" the aliens that he had available as well. From the cartoon point of view, it was the Omnitrix giving Ben a random assortment of aliens to choose from out of the 1 million plus available.

From the producer's point of view, new aliens means new merchandise (toys) to sell. And since the old aliens still show up from time to time, those toys will continue to sell. So, adding more aliens means adding more toys.