It's an extremely un-European approach. European companies normally ignore their paid customers too from May to August.
Of course, "European companies normally ignore their paid customers too from May to August" is factious, but there is a slight hint of truth in there, in that things generally is slower, at least in the South/West countries I'm more familiar with.
That is not ignoring but announcing a delay.
Bigger companies may have only limited number of people checking the mailboxes in july and august, that doesn't excuse not sending a small reply announcing delays but I guess they take it so much for granted they don't realize other continents aren't used to those kinds of delays. However in May and June every company is totally operational ( that doesn't mean nobody take holidays ). If you request something to one named person, that sole person can have scheduled holidays, parental or medical leave any time of the year. If it is a team mailbox, you should get an answer.
I think maybe with the American PoV of "the customer is always right", that might basically feel like a slap and the face and being ignored. Of course, we should understand that every human needs to rest during the year, but if you don't have that opportunity yourself by law, maybe you're less knowing about that being a thing in other more modern countries?
Every once in a while there is an exception. Then that guy says "If your sending me to Australia I'm going to use my vacation to scuba drive the Great Barrier Reef" - and his body is never found. True story, it took months for someone else to figure out everything that guy knew.
So every single business, everywhere in American, has at least two full-time employees or at least one other backup that is available when you want to vacation and the stores/businesses never close? I'm guessing the ones that don't have that (if they exists), just never have vacation, or how does that work? Sounds like a fever-dream, but I guess if that's what your experience tells you.
Stores remain open because they ensure somebody isn't on vacation and thus able to work. They sometimes give extra pay if you work a holiday (this is rare though - generally there is somebody who wants the hours/pay more than this holiday off - they can take time off a different day).
For small business (think a plumber) it is common to arrange a competitor who will take care of your emergency customers needs.