I think there's multiple issues here. First is the fact that many juco programs just don't have the necessary strength and conditioning staff and facilities to prepare a player like the Power 5 programs have, including nutritional support. Players are sometimes more like freshmen than juniors in strength and conditioning. That's why I prefer taking jucos who still have their redshirt year available.
Second, the player may have come into a level of competition that he just isn't prepared for physically or mentally. The SEC is the biggest of the big time. I am unfamiliar with the program Williams came from although they seem to have a solid program with several NJCAA All-Americans. But most of the jucos in the SEC tend to come from the Mississippi, Oklahoma, Texas and California programs. Lackawanna seems to be more of a Big 10/ smaller Big 12 (West Virginia) feeder program. It's a private school with 1800 students and tuition is $13,000 a year.
Finally, Pruitt was desperate to just get some large bodies on the line and may have been forced to either play Williams before he was ready or take a player he wouldn't take today.