I presume because the list of potential people who you could connect to might change.

I guess they could re-scan it on a schedule but that wouldn't solve your issue and might annoy their user base who are using it because it "just works."

Plus removing a permission isn't something any app supports that I am aware of. It isn't even something you're meant to be able to do on Android.

point being, it's a stupid idea. every half decent programmer would just update the diff.

Nope, I wouldn't even consider that. Firstly because K.I.S.S. and secondly because you've exchanged a relatively small data "cost" with a much larger storage and processing "cost."

You've had to have a database of everyone's contacts and then be comparing X with Y every few connections...