Mom and pop shops were not much better on average. I've been in a few that are many times better than the big box stores (even in terms of price). I've been into many more that were inferior to big box stores in almost every respect. Notice the use of tense. While some of the inferior stores survived, many did not. A lot of the excellent stores didn't survive.

Businesses have to adapt to stay relevant. You typically get better service out of mom and pop shops these days because good service is cheap while bad service is costly. (Basically, you overcome sloth to keep customers.) Big box stores will have to adapt too, likely by becoming more efficient and improving service.