Persistance Ignorance and REST

Persistance Ignorance is a key pattern to achieve efficient functional testing. I believe it should apply to infrastructural purposes in general. However, it seems this guideline is rarely followed in WOA, especially with REST APIs. As REST seems to be a data-centric architecture, I do not understand why PI does not apply to WOA in a more popular manner, to prevent systematic and expensive end-to-end testing.

Is there any kind architecture or practice that could ease the introduction of PI into REST architectures ? Based on your experience, did you try to follow the PI principle in your REST architectures ? If not, why ?