The NCAA put the transfer rule in place to hold baseball coaches and athletic departments accountable for players not graduating due to consistent transfer in and out of programs. It had the worst graduation rate in all of college sports.
Teams now have to meet performance goals through the annual performance plan, aka APR.
Plus, as told to me a while back, coaches had trouble keeping their teams competitive. There was also a lot of coaches having their players recruit for them during the summer, which is a NCAA violation.