I don't think that "it happened" to the whole Big East. The Big East was composed of several blue-collar football teams who could beat you if you underrated them plus the West Virginia Lightning Show [and previously, the Louisville Scoring Machine]. The fact that WVU could roll out on the field in those years and have no fear whatever for Miami, Florida State, Oklahoma style athletes was unique in that conference. When football's mighty looked down at the other end of the field and saw White-Slayton et al, they thought "My God how are we going to contain THAT!!", and they didn't. WVU's lightning gave a prestige to the rest of the conference that even Kelly's Cincinnati wasn't quite able to do.
So what happened?? Rodriguez left for Michigan. Behind him he left a team that he was already tinkering a bit with to allow White to pass more, but when Bill Stewart [a family friend, by the way] took over, he and his OC began turning WVU into a "standard offense" with a passing QB and a lot of TE and power running involvements. The more WVU standardized, the lower the offensive output has become [WVU is saved nowadays by a tremendous Beamer/Foster-like turnover defense--DO NOT underrate THAT part of them].
Over-all this trend has lessened WVU from a potential challenger to a just-good team, and believe me WVU fans aren't too happy. When Louisville fell apart, largely due to coaching malfunctions/transitions, Ray Superman Rice left Rutgers, and Kelly then left Cincy, all you have left is the blue collar lunch bucket crew---still tough people but not top ten teams. There's no DAZZLE left in the Big East, and that's the type of coaches there.