A lot of people who were looking for a more grounded story set in the star wars universe got what they wanted.

For mainstream viewers, it was boring because it didn't have any of the instantly recognizable characters or settings. We didn't have the force. Other than Andor and then Mon Mothma, every other character was new and had to be introduced. Unlike a movie where you had to tell the entire story within 1.5-2 hours so you only really get 20-30 mins to introduce the characters and their motivations. Instead,we get a long drawn intro to our three main stories: Andor with his path to rebellion and the rebellion from the point of view of the ground soldier, Deedra Meero and the empire's perspective, and Mon Mothma and the rebellion from behind the scenes.

The long character and environment development is important to really have the huge payoff for the finale when all 3 worlds collide on Ferrix.

This is so much different because the mainline movies are much campier and more action packed and less grounded character drama set in the star wars universe.