I thought he was a UT commit at one time.
No. He committed to Clemson in December 2016 as a high school junior. Tennessee offered him when he was a sophomore, and he stated from his first days in high school that Tennessee was the leader. But apparently Butch and staff didn't pay him much attention until his junior season. By that point, the damage had been done.
We can all speculate about why Butch dropped the ball on Lawrence...but it's a pretty easy guess that Butch though he had Emory Jones in the bag. Jones was the top-ranked dual-threat QB in the '18 class, he fit Butch's infallible offense better than Lawrence, and Tennessee was the leader all the way. If Urban Meyer hadn't offered Jones, he would've committed to Tennessee. Of course, he wound up flipping from Ohio State to Florida, so he may not have been attainable anyway.
My guess is Butch was all-in on Emory Jones, believing he was going to land him, until he lost him. Then he turned his attention to Lawrence but Lawrence had no interest in playing second fiddle, regardless of how much he liked Tennessee.