DuffMan,
Do you not believe the relationship Mack has with Texas HS coaches is important to our ability to recruit?
John Mackovic never bothered to establish a good rapport with them, and look at how many of our top Texas players were going to Michigan, Florida, Miami, UCLA, OU, Nebraska, Colorado, and Tennessee (those were the prime out of state raiders just going by memory, there may have been others I'm overlooking) during his time. And look at his record with the kids he did get.
So to answer your question why? Because it's smart. The HS coach may not make the final decision, but you can bet your *** he'll communicate his personal feelings about Mack Brown and UT to his players. I'd much rather have a coach saying good things about our program than bad, because you never know how much influence that voice may have in any given case.
And yes, those coaches have egos, and they can get their feelings hurt by having a coach from UT bypass their star players in favor of some kid from out of state without being given a good explanation as to why that's happening. Good explanations can include that the OOS kid is clearly more talented, has better grades, is a legacy, etc. But if that coach feels like your program is ignoring his kids, he may start steering them to schools he feels are more friendly to him and his program.
If that's ******** to you, then so be it. It makes damned good sense to me.