I think the OP's point is that the upper DH/(Keystone Select now) boundary was recently (last year or two?) extended upstream from the mouth of Bailey Run to the 872 bridge near the confluence with Schoolhouse Run. I checked the 2018 reg book I had handy and the upper DH/KS limit then was the mouth of Bailey Run, FWIW.
I'm assuming the OP's BIL's cabin is somewhere upstream of Bailey Run, and downstream of the 872 bridge, and he and his family liked to fish bait and/or creel some fish while at their cabin. If I owned that cabin, and liked to fish bait or keep some fish earlier in the season, I'd be pissed too. Glotown, correct me if I'm wrong on those assumptions.
That said, the PFBC can't account for every individual landowner's personal opinion. Yes, they should ask, and survey, and probably did. If the majority of those landowners upstream of Bailey Run, and downstream of the 872 bridge wanted this, then so be it. The OP BIL can certainly post his property in protest, nothing wrong with that...A byproduct of changing regs I'm sure the PFBC weighs out when making these decisions. Perhaps there were more landowners who would have posted, or were threatening to post, had these changes not be made? (I have no actual knowledge of that, just making a point that the PFBC does consider this stuff in their decisions.)