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?