One of the peculiarities of Texas is that it's normal for people to drive 5-10 MPH over the speed limit while on the interstate. Provided they're not doing a speed trap, the police generally don't care.
Another of Texas's peculiarities is that most drivers don't respect reduced speed limits for construction zones unless there's a speed trap or it's dangerous to go normal speeds.
As a result, if you drive the speed limit, you can conceivably end up driving 15 mph slower than everybody else in construction zones. This is unsafe for you and everybody else on the surrounding road.
Say that you're going the speed limit, and someone hits you because you're going 15 mph slower than the prevailing traffic conditions. Are you liable? You're following the speed limit, but by doing so you made yourself a danger to those around you.