I definitely agree about the big companies. They have style guides for this and it’s definitely about perception. However, the formal you sounds very stiff and official to me coming from people who are very friendly and informal on the phone and who are in many cases older than me. At the same time I realize that some of their clients might appreciate the formal form and they’re just using it by default instead of overthinking it.

In my experience many small businesses use it in written communication. Even if you just had an informal phone conversation with them, they will follow up with a formal email. GPs do it too in online written consults. I find it slightly annoying, because it forces me to consider doing the same, which I rarely do otherwise.

Sometimes younger people (strangers) address me in the formal form, even though I’m in my 30s.

Big companies usually use the informal form in their communication.