In the UK there has been a move away from giant supermarkets over the last few years. The consumer electronics and other non-food items that pad out the giant supermarket and make it hard to get to the milk, people buy that stuff online now so it is not possible to 'pile high' in the big box supermarkets.
With this move has been a growth in convenience stores that are operated/franchised by the big supermarket brands. People go to these places for their milk. (And do a big online shop for the bulk of their groceries).
So people are just deciding not to go to the big box stores in the first place.
Anecdote, but this happened to me. Where I was living the largest 'Tesco Extra' imaginable opened up literally across the road. This was AMAZING. Well, not really, within a week we were back to the convenience store buying everything there, it really was too much hassle going to the giant Tesco. Didn't need the kilometre walk past the TV's, clothing and other stuff that was placed between the store entrance and the milk. The 24/7 novelty wore off too, didn't actually need to go shopping for that pint of milk at 2 a.m.
Another part of the problem was that the customer service in the local store was more friendly. They didn't have people to greet you or people giving you free samples or any coupons at the checkout or any loyalty cards. Just polite 'how's your day?' chat with the small team of staff - all known by name - sufficed.
With the big supermarket I don't think there was this inate customer service aspect, 'customer service' was contrived marketing, nobody cared about you. And so it is online. People that do marketing online care more about their Google analytics and loading up websites with spam-scripts than they do about 'reality'. They may have one result per quarter from that pop up, that extra sale is good, a result, success even. Not on their dashboard is how many people didn't buy because of the stupid 'enter email address now:' popup they had on there. Marketing people are not the sharpest knives in the drawer, far too often they lack the skills of empathy and cannot see things from the customer's perspective. Hence they have to use things like statistics in an attempt to make up for their lack of intuition and appreciation of customer service.