We call it the "North Texas Curse" ;-)
I think there are several variables involved in what you are talking about and what I've witnessed all of my life living in this area.
The first one is that the dryline sets up pretty far west of here about 90% of the time, so the storms have a long ways to travel and end up losing the better instabilities around peak heating if they do make it this far. Most severe weather events initiate from around Abilene to Wichita Falls and westward....unfortunately. ;-)
The other thing is that most mid level impulses and shortwaves skirt the area by travelling from W TX into OK or KS. This has been especially true for quite a few years now in our new "climatology" which consists of early and strong ridging setting up over Texas. It's been a frustrating pattern since 1996.
I also think that sea level elevation has something to do with it as well with storms moving from higher terrain into lower.
But above all of that, it's because I live here. LOL
That's my $0.02 worth.