Could someone explain to me why it matters?
It doesn't really matter, but as long as a largish amount of people thinks it does, then it does sort of matter, to a certain degree. If that makes sense?
For me, it doesn't matter at all really, it only becomes significant if someone believes themselves to be working class, or middle class, or upper class, because then they judge you using the same system and have certain expectations of themselves and you.
Probably.