I obviously don't live in PA anymore either; nor does my 1/2 dozen fishing outings in PA/yr/boots on the ground make me anymore than an armchair expert, at best, on the realities of your streams.
That being said, I think it boils down to mostly to the effort required to fish a stream, and the reward. This, is of course obvious. I am not saying most people are lazy, or even that its 'more cool' to 'blue-line' (even though it is! LOL), but after changing my trout fly fishing interests/habits several years ago to generally seek opportunities in smaller, more 'natural' streams, the evidence and experience of 'pressure' on these waters, anecdotally for me, is far less than I see on a Fishing Creek, or Little J. And, its a strong function of how far you have to walk in to get on that water, followed next by a perception of numbers of 'available' fish. Many folks won't spend time on a stream they feel isn't well stocked , or 'populated' with an abundance of 'catchable' trout.
For example, on the stretch of the Laurel Highlands I like to fish, say within a 'triangle' formed by Clearfield, Tyrone, Somerset, even with issues like acid mine drainage, smaller watersheds, population centers, etc there are streams with little to no noteriety that anyone could access on public lands, and I'd bet have a good day fishing. But, other than worn paths near a trail head, or at those first few pools, the overgrown trails and my lack of encountering other fishermen tells me these 'quiet' streams may be just that: 'quiet'. Not 'secrets' mind you, just 'quiet', because for a portion of the fishing public, they just aren't worth the effort. Even after that surge of COVID/post COVID social media coverage of 'blue lining'.
Joe