Does anybody know why there are really no customizations for the 98 to 02 GM (headlights, tailights etc.)

 

Probably can't find those lights for 2 reasons --
1. Limited production. Not many of these cars were made in the first place.
2. Geezer cars -- there was very little demand for trick lights.
Go HERE for trick headlights:
They have trick lights for a lot of vehicles -- I got some really cool headlights for a Jeep Cherokee from them.
Amazon has Tail-lights, too -- a plenty to choose from, but they look like the stockers.
Good Luck.