The death stranding, or…?

Completed the game and now I understand that the death stranding occurred prior to Sams birth, and as I understand it (speaking generally) that the death stranding made it so that people who die get stranded on the beach, can’t make it to the seam (and thus the afterlife), and get stuck in the physical world as BTs.

What I’m not understanding is exactly what changed when Bridget brought Bb back to life (outside of the creation of DOOMs sufferers). The game implies that her bringing BB back to life made BTs appear in our world, but wasn’t that already the case since the death stranding had already happened? Hope the question makes sense.

Also love this game so much.