Because she would have exactly 0 college coaching experience, 0 head coaching experience, 0 recruiting contacts and worthwhile knowledge of the collegiate recruiting landscape, and because of all that, there would be scores and scores of more qualified individuals. Tennessee shouldn't be so desperate for a coach that they hire someone whose resumé reads, "5 years of NBA assistant coach", and that's it.
She may have a great deal of basketball knowledge, but she would have to hire a staff that would kill it in recruiting. Finding that kind of staff willing to work under a woman in a men's sport may be challenging, and maybe it wouldn't, but an AD would be putting his career on the line to find out if it would work. All kinds of stereotypical hurdles to overcome for Lawson to be successful in addition to the tangible hurdles I already mentioned. No way she is even dreamt up by anyone in our fanbase if she didn't play for Tennessee.
She would have roughly the same kind of experience Juwan Howard had, and an ounce of the national notoriety. In addition to the stereotypes she would be fighting, I just see no way that she is the best choice for Tennessee basketball, and if we, as a program are forced to dip that deep into a pool of candidates, then the AD should be fired, too.