I don't recall Apple ever "insisting" anything about glossy vs. matte. They simply eliminated the matte option without comment, and finally brought it back many years later.
If you have a reference to a public statement from Apple defending the elimination of the matte option, I'd like to see it.
To be clear, I've been complaining about glossy Macs ever since matte was eliminated, and I too purchased an M4 MacBook Pro soon after it was available.
Wasn’t the matte option that disappeared just then removing the glass in front of the screen? I seem to remember that (my MBP from that time was glossy).
The nano textured coating they are using now is quite complex and I am not quite sure it was applicable at such scales cheaply enough back in 2015.
A glossy option was introduced in 2006, but the MacBook Pro was still matte by default.
In 2008, the MacBook Pro case was redesigned, and then the display situation changed significantly.