Because the event is one of the most stacked of all time, despite hardcores complaining that the card sucks (not sure if they're still doing this).
As for why...
Cody Garbrandt from the UFC's perspective is past it. Figgy is past it too (due to age).
Look at the least stacked cards on the prelim card:
Sodiq Yusuf vs Diego Lopes. Both younger guys, high potential to be future elites and stars (due to their exciting styles) of the featherweight division.
Kayla Harrison. Good potential star power as an elite female American athlete, who knows how to talk in public. Can be marketed to casuals as Ronda 2.0.
Aljo vs Kattar: If Aljo wins he might be next for the FW title.
Main card:
Bo Nickal vs Brundage is the only one that isn't a title fight or a potential #1 contender fight. Again, like Yusuf, Lopes and Harrison, Bo Nickal's a future potential star and elite of the division, rather than having his best competitive and star power years most likely behind him, like Cody and Figgy.
The other fights are all between higher ranked fighters that any fights on the prelims, only prelims fights that are close are Jiri-Rakic and Marina-Andrade.