Is the reason there isn't a wild pheasant population in PA. because of the lack of habitat or are there other issues? Lack of habitat has hurt all upland game populations. The only way that we will have the numbers of birds as we did back 50 years ago would be providing more stable nesting, winter shelter and small grain food sources. As the quote from "Field of Dreams" movie implies - "Build it and they will come."
It was a combination of factors that slowly eliminated the wild pheasant population in PA over a 20-25 year period beginning in the 70's with the banning of DDT and passage of the Endangered Species Act in 1972. Prior to that birds of prey were killed on sight and DDT was making eggshells soft so that chicks never hatched. Raptor numbers began to increase significantly and in the 80's the Game Commission even stocked ospreys and then eagles to reestablish extirpated populations.
In the late 60's to early 70's there was an Avian Flu pandemic that wiped out hundreds of thousands of pheasants along with millions of other bird species.
In the early eighties clean-farming became a thing. The thick hedgerows that typically bordered small fields were buried to create large tracts of crop fields with no cover available for small game. During that same time period the fur market crashed and lots of folks quit trapping.
So now you had a major increase in avian predators, a major increase in terrestrial predators (coyotes started becoming a thing in PA in the 70's) and a huge loss of cover for pheasants to hide in.
Also in the 80's and hybrid grasses were developed that allowed earlier first mowings of hay fields. Hay fields were a favorite nesting location for hen pheasants. Early mowings meant hens were still sitting on nests when the fields were mowed. Hens would stay on their nests and be killed when the mower came through. That meant the loss of the entire nest.