Almost like the rules for taste are made up on the fly…

Of course they are, taste is a social conversation to align for a window of time on a set of guidelines. Taste is a social construct, being a social construct (or "made up") does not make it any less real or valuable.

It’s a social construct yeah, but constructed by what?

IMO most of the unpleasant truth about taste is that it is really a stalking horse for money and distinction (cf the book of the same title).

Taste isn’t a social construct, it’s a function of how your brain is structured/wired. How it’s applied is a social construct.