Other teams/programs have gotten better, relative to BYU, and competitors have discovered that there are lots of good football players who have connections to the main groups (I assume) BYU recruited from heavily - the state of Utah and the Polynesian community.

Since the Lavell days: the Internet and social media have made it easier for recruits to be noticed nationally; in many of these kids' teenage (and younger years) the Utes (or other teams) have gotten better relative to BYU; Utah joined the Pac 12, which brought bigger programs in state to play which opened up the state for more recruiting; "blue blood" programs started recruiting in state (USC, AL, tOSU, ND, etc.); LDS coaches (or coaches with connections to the state) have become more prevalent on coaching staffs around the country (Stanford, USC, TN, etc.).

Coach Edwards has been away from BYU for ~two decades. That's a long, long time and a lot has developed since he last coached.