First of all, Greg Winslow was and is a dick (my opinion only not necessarily his swimmers), and his methods were questionable and not particularly successful. His biggest problem (besides him not being an effective coach) is inconsistency in the treatment of his athletes.
I know for a fact that Karson Applin and Matthew Fiascone were kicked off the team (I believe for drinking and for other offenses) sometime during the 2012 season. Since then, Fiascone has been going around and stirring up trouble, finding students who transferred or quit, and collecting their stories and releasing them to the media. This article is the culmination of his efforts.
That said, Winslow was inconsistent. He kicks Applin and Fiascone out for drinking, yet provides beer for other students, and attended events where his swimmers were imbibing. So what's the real reason that Applin and Fiascone were dropped? Because they questioned his methods and didn't suck up to him the way the other swimmers did.
So Winslow was released because of the sex with underage swimmers charge, but I think that was only 10-20% of the problem. I think the other 90% was his dictatorial style and his autocratic policies designed to, according to him, build team spirit, but according to me to build blind unquestioning loyalty to him and he alone.
Some of the weird crap I saw (weird in my opinion; the swimmers didn't seem to think much of it.) He would tell his swimmers (female only) when they could shave (their legs, their pitts, everything.) During peak training week he would call practice at any time of the day, from 5am to midnight. He wouldn't give advance notice, he'd just text the team and everyone had to be in the water within 10 minutes no matter what they were doing. He'd make the women run the campus in just their swimsuits and shoes during the day, when school was in session. WTF? Do you know how painful it is to run without a bra, and I'm not even talking about the psychological trauma of running around in front of students dressed in nothing but a thin layer of lycra. He inculcated a hatred of BYU in his students, so much so that no one on the team owned anything blue other than jeans. Why the hate? The football players don't even hate each other.
I believe that Chris Hill knew nothing about this. As others have said, he was protected by his people, and nobody cares what a swimmer has to say. When it finally broke, he did interview 50 people, and supposedly no one corroborated the story of the disgruntled athletes. However, this result was discovered when all the swimmers got together and discussed what they told Hill. If I were a swimmer and I did agree with the charges, I sure wouldn't have claimed it.
I think Hill's people did him no favors by hiding the extent of the charges, and claiming that it was a few disgruntled swimmers. In the midst of his Pac12 orgasm, he wouldn't have had any time to really investigate the extent of these charges, and his people led him into believing there was nothing there. I believe that had Hill known the extent of what was going on, he would have absolutely stepped up earlier. He is now going to find out that the Pac12 doesn't allow for ignorance the way the MWC probably would have. I don't believe that Hill should be fired, but the Pac12 comes with a completely new set of politically correct expectations, and swimming is a Pac12 marquee sport.