I don't see a fix to this. As long as people can profit from selling their tickets they'll keep selling them. In fact, I'd bet there are several thousand season tickets that were bought just for the opportunity to make a profit. Some probably not even sports fans.
I was a season ticket holder for 18 years. I did go to every game but there were 2 seats to my left where I never met the owner of those seats. Someone different there every single game (sometimes no one because I guess they weren't sold) and about 50% of the time they were fans of an opposing team.
As long as there is the kind of demand there is for tickets, this doesn't get fixed. Houston, however, isn't nearly as bad as it is for Arizona or LA. Dallas has a ton of opposing team fans. Vegas too. It happens all over because a nice profit can be made.
It also doesn't help that it costs so much for the average fan to attend all the games. At the end it was costing me over $200 per game just for 2 tickets and parking. And my seats were upper tank. So even if you are a diehard fan, if you can make half your season ticket price or more when good traveling fan teams like the Steelers or Packers come to town, even a lot of those people will sell.