Actually when you hit max level in BL2 the numbers also stop popping out.
Be happy they appear in BL1. I wish they did at max level in BL2 and 3 also.
They are a great visual indicator that yes, you did kill that guy. Many times in 2 and 3 I waste a few shots and a important fraction of a second still shooting an enemy I’ve killed, but it’s death animation is slow or overly complicated and it takes that fraction of a second to confirm the kill. And of course in BL3 there’s so much visual clutter that you simply can’t see if it’s dead.
The numbers still popping in BL1 mean yeah, you killed it, safe to move on, and I like 'em.