UAB was trying to get the motions going to build a new stadium and get out of Legion Field (which is a shit stadium in an awful part of town and certainly hampered their program momentum) as recently as six months ago.
There is one board of regents that runs the entire UA system, and it is (predictably) chock full of UAT alumni. They've pulled every string they could possibly pull to implode UAB's program, and this, more or less, was the nuclear option. It has been nasty as hell, and I expect it to get worse; it will include lots of lawsuits and maybe even a full on split between the two systems. UAB sure as hell doesn't need UAT, as UAB's grad programs, especially the medical school, bring in enough dollars to keep the coffers flush for quite a long time.