Pro Football and College Football 1970s Question

[Venson]

I thought this may be the best place to get some insight from the older board members who really know a lot about football in the 1970s. Being a Pittsburgh Steelers fan since about 1978, which is the earliest I can remember watching them, I decided to do some research about the Super Bowl 9 team. As I was looking at their roster and looking at the replay of the game on YouTube, I noticed that 12 of their starting 22 players came from schools that are considered non-P5 today. Two of those starters were UNT players in Joe Greene and Ron Shanklin. I also noticed that more than half the roster of the whole team came from schools that are non-P5 today. I guess my question is with so many players back then on a Super Bowl winning team coming from non-P5 schools, was being from a P5 not that big of a deal as it is today? If it wasn't, what is the reason for the big disparity between P5 and non P5 today? Or was it as big of deal back then and the Steelers were just an anomaly? I kind of noticed the Cowboys of the 70s also had quite a few players that were not from P5 as well.