Why can I only see estimated PAI scores for runs in the next week?

The PAI estimation becomes much less accurate the further into the future it looks. It won’t know what other activities you’ll do which will affect your PAI score, only the workouts you’ve planned, so it won’t have a clear idea of what your PAI score will look like to make an accurate estimation too far in advance. Also, over the course of a training program, you should be getting fitter! This means that the same workout might give you fewer PAI points a few weeks from when you start, because you don’t have to work as hard to complete it. Making an estimation closer to the workout means it’s much more useful and realistic to you.