Family. Money. Recruiting.
McCasland is a native of the Dallas/Fort Worth metroplex. Both he and his wife still have family there. He made $350K at Arkansas State with state income tax, and I'm told he will make $650K at UNT without state income tax. UNT is also located in a fertile area for hoops talent, and it should be easier to keep some of those guys at home compared to getting them to Jonesboro. He also has a connection with UNT COO for Athletics Jared Mosley, who was Abilene Christian's athletic director years ago and hired McCasland there. (McCasland left four months later for an assistant job at his alma mater Baylor, where he was for several years before going to Arkansas State.)
After getting the Arkansas State job, he convinced some good players to stay (one did end up at Texas Tech as a grad transfer) and won after adding some of his own quality recruits. I expect him to do the same at UNT, although the program is in bad shape. The Mean Green have some talent, but they never meshed under the last coach. If he can keep the roster intact, add some recruits that fit his system (versatile and athletic) and get everybody to buy in, we might see UNT have a nice turnaround season in his first year. Regardless, he won a junior college national championship at Midland College (former Cajuns guard Ryan McCoy played for him) and coached Division II Midwestern State to the Elite Eight twice before posting a 20-win season with the Red Wolves, so he clearly can coach and I'd expect him to get UNT back on track soon.
I've known McCasland for a long time and thought Arkansas State made a great hire when they got him. Feel the same way about him taking over at UNT.