[extra88]

Yes, my recollection was wrong. There are some landmarks that can be nested inside other landmarks and still be conveyed but <header> (ARIA role "banner") isn't one of them.

Using <header> elsewhere for developer convenience is fine but that's all it is.

Headings are especially helpful for screen reader users are especially helpful but their value for sighted users are often underestimated. Developers think that by putting something in a box and by its styling that people will understand what it is, what it's for, when using a heading to put a name on it would be very clarifying.