There was a time when the show was the UFC's crown jewel, their lone TV product and their biggest promotional tool. The first season of the Ultimate Fighter is almost solely responsible for how big the UFC has become. Now, it doesn't even serve a purpose, but it has kept plodding on.
In 2006, Tito couldn't beat Chuck on his best day, it just couldn't happen. Chuck knew it, Tito knew it, most everyone knew it. Tito knew it to such a degree that he spent years telling everyone he and Chuck were friends, so as to avoid fighting him. No iteration of Tito Ortiz could beat Chuck, until now.
In a vacuum, Shamrock/Horn might not seem like much, certainly compared to fights of today it pales, but at the time it was almost an aberration, in much the same way that UFC 17 was. It was the start of a new wave. So, it is fitting that we look at the main event of the card that night, at least for the fans in the arena, and see what the future of MMA, or more appropriately NHB, could be in 1998.
Update: I wrote this before the UFC announced TJ-Cejudo for the Flyweight title, so who knows how much of this will be relevant down the line. There is a good chance that fight is the last in the division anyway, but who knows. But, I think a lot of it still has some bearing.