The model of 'time travel' deployed is specifically anti-paradox. Sort of like dry sheets enabled. Thanos has a paradox, but that's what he gets for Doing What He Did and Stones Adjacency.

Steve's just been in however many alternate realities that diverge at the point he joined them already in progress. Though somehow he comes from those to the bench but I'm not sure how 'sticky' they're supposed to be. Or if he got Pym Particles, an Alien Life, Tardis assist or ran into the Sliders crew.