They are mostly catering to the local auto repair shops around here. Free delivery, and special pricing based on last month's volume. We had several accounts at different stores (because not all the stores stock the same stuff), but they all went to a different pricing model to "reward" their loyal business customers (and it does make sense). They would match online pricing IF you had a good relationship with them.
Also, most local auto repair shops are using purchase orders and putting bunches of parts on order with one PO, and the customer's car is in the "wait" area, so time to delivery isn't quite as high priority as to a DIY guy who is currently not running because of a specific part. Having said that, some repairs need common parts, and that is what these brick and mortar stores do best - Batteries, hoses, oil, filters, brake parts, fluids, etc.
So, they fill the right need for local auto shop (which is the higher volume, higher total profit, constant business) and make more money in the long run this way. That's why there are so many of them and they are everywhere. If there wasn't money to be made, they wouldn't be able to stay in business.
In the long run, the business model they are using may have to change if the local repair shops start to "dry up", because then their base of business will be moving away from them.
I believe the current business model makes the most sense for the brick and mortar stores as the DIY market is dying due to manufacturer's making it harder and harder to repair your own vehicle, and most vehicles now need very minimal maintenance anyway. Shoot, the newer electric cars (Tesla) need almost no maintenance at all - so the brick and mortar stores are reading the writing on the wall and moving their business to the "guaranteed" business of the local shops and away from the "walk-in'" coming in from the street.