There's a similar situation between Czechia and Poland currently. Folks from .cz travel to .pl to buy food, cigarettes, medicine and even coal. I have no comparison of goods quality, but Poland is cheaper for Czechs.

Cross-border shopping used to be a big thing for Danes as well but mostly for soft drinks, alcohol, candy, and petrol. They all used to be a lot cheaper in Germany but that was because of our taxes in Denmark. It was our own bloody fault.

There are Danish supermarkets right across the border in Germany for the locals because things are still a bit cheaper there but most of us no longer bother driving all the way to Germany with a trailer on the car just to buy stuff. It used to be common to do that a couple of times a year.

"I don't understand why food would be more expensive in countries with lower wages."

The multinationals do what they can get away with. A fine from a Bulgarian authority is likely to be trivial to them, and if it actually bites, they can always withdraw from the market as a retaliation.

No one wants to lose market access to Germany, but the smaller countries don't have as much leverage.

It's still a thing. A lot of people in Croatia still buy specific food products in supermarkets like Lidl and Muller because they carry the same products as in Germany or Austria. So of much better quality of course.

The price at the time is generaly considerably higher than in neighbouring countries because VAT is just a part of the general taxation scheme. Whatever taxes companies get saddled with just get transferred to the general population via prices on the stuff they sell. And taxation in Croatia is crazy high unfortunately for everyone.

And in Switzerland Lidl is basically looked at incredibly low quality food provider.