Why are both Bucks and Berks county PA much more GOP friendly than Chester, Delaware, Leigh, and Montgomery counties? Even though Bucks didn’t vote for Trump either time or was very close both times.
Berks is an easy one. Reading is a separate metro from Philly; it's similar to Lancaster and York as a lowland, more ag-oriented mini-metro with heavy Pennsylvania Dutch influence. It's on the edge of being swingy because Reading is a fairly heavily ex-industrial place with a large Latino population.
Bucks is a bit more complex. Lower Bucks is similar to NE Philly in that it's an inner suburban swingy area with a lot of more working-class white people, similar to places like Nassau County except less diverse. The central part of Bucks is a bit more upscale and liberal and votes like much of Montgomery County, but the far west is fairly exurban and consequently R-leaning.
But even then Middle Bucks isn't even close to as liberal as Montgomery even it has similar demographics. The lack of the main line is probably a key influence.
