The mirror's angle can change, while driving, in such a way that pulling over to stop and fix it isn't the safest option. With dedicated tactile controls you can adjust mirrors without taking your eyes off the road, while also verifying that the mirrors are adjusted correctly.

I think the number of people who can say that they have never needed to adjust mirrors while moving, even after having spent a few minutes adjusting them in the driveway, is very much next to zero.