Tailgating for Titans/Texans Game Questions

Hey there! A group of about 15 of us wanted to tailgate the Titans at Texans game on NYE but we can only find parking pass but not tailgating passes. We aren’t interested in game tickets, but why is it impossible to find tailgating tickets? It’s been several years since I did this but do you still need tailgating passes?

Any help is appreciated. Hoping for a W to help our playoffs chances!