that's part of it plus even 4-3/3-4 defenses have merged a bit and look the same.

But even in base D, the 4-3 DE and the 3-4 OLB have a similar skillset, rushing the QB and playing on the edge in the run game, therefore "edge defender" makes the most sense

— Steve Palazzolo (@PFF_Steve) July 30, 2019