Max Hall, Taysom Hill, Jan Jorgensen, and Andrew Rich were all transfers and are
among some of the best to play at BYU.
Bronco also had a long list of transfers who made a significant impact for the Cougars, many of which transfered from P5 programs.
Kalani has done well in this respect as well, but it is nothing new. Disgruntled talented P5 players who are unlikely to start often look for a place where they can get playing time and possbily even catch the eyes of NFL Scouts.
BYU is one of the highest profile non P5 schools out there, so they are in a prime position to catch those defecting players (assuming the players think exposure is worth having to obey the honor code).