A person I am close with once worked at one of those mattress stores. They get maybe 1-4 sales a day, but they have stupid high margins and pay their workers poverty wages.

I know a town with I think five or six large furniture (or general household item) stores basically next to each other. Big brands.

It is probably a combination of factors: The area is easy to reach by car, it's easy to supply by truck, plenty of space for storage and people actively come there to shop furniture - yes you will be competing with five different stores, but since the customer base travels quite a bit anyway, you'd be stupid to set up shop in a different town. People will walk/drive 5 minutes to check a different store if they already came all this way, but they probably won't head to a store two towns over just to compare prices.

I think it's the same thing with sofa/couch shops. I have four of them at a walking distance near my place. I've never seen anybody going in.

Also, an Italian company which I won't name is always advertising on all national TV channels. All the time. TV ads prices are insane, how can they afford them?

In the 70s, the police made a famous mafia family "split" and move from the South of Italy to some North cities, in a futile attempt to stop their mafia activities. A branch of this family opened a mattress factory, which is now famous all over Italy. This is not speculation, it's history. I won't name this mattress factory, but if you can read Italian you can Google "mafia Budrio" to learn more.

I have to imagine matrices are a high margin item because of how infrequently they are purchased, how they cost as much as some used cars, and how important in-person examination is. Perhaps there's some kind of vendor lock in similar to car dealerships?