I don't think the 2002 defense was as good as generally believed. The fact that they stayed healthy and the starters helped mask their shortcomings.
My proposition is that teams didn't challenge the Texans 2002 defense as much as other teams, because of the inadequate Texans' offense. For example, in a third and short situation, teams could try to run for the first down (not risky). If they didn't get a first down, it helped the Texans' defensive statistics, but it didn't hurt the opposing team. Not infrequently, the Texans' offense would go three and out, might even lose yards and give the ball back anyway. Why take a change and press the Texans' 2002 defense?
Just a thought.