Where do you live that has garages open on a Sunday morning? I don't think I've ever seen a tire shop or auto repair place (other than the big box and wholesale warehouse places) that's open on a Sunday.
I decided to take a very non-representative sample, and found that in many (but not all) parts of northern California, locations of the chain tire shop that I use are closed on Sundays, but most locations in the LA area are open 7 days a week. This chain has a lot of locations. It could be that they're responding to what their competitors do in both cases. So maybe getting tires on Sunday is a so-cal thing? TBH, I personally am more used to expecting the tire shop to be open 7 days a week, unless it was a small, locally-owned place.
LA is an anomaly. Most places are 5-6 days a week, tops. Around where I'm at currently, if the place is open on Saturdays, they're closed on Monday to compensate. There's a lot of those
