I think it's to do with string tension/thumb position. It's what makes me always wonder when I see playing in the p pickup position. The string is floppier there so moves more which I find makes it harder to play accurately with a nice tight, focused, controlled tone. Playing back by the bridge on any bass results in less string movement so less controlling the string and a quicker more precise, under control sound and playing experience.
Ime imv IMHO ymmv etc