I think that happens when the thread appears in active, so people come on who really don't care about style, so they pop up and tell everyone that, which isn't especially helpful on a thread about style.
I think Mumsnet can stop threads appearing in active, but that also wouldn't be something everyone would want.
Here's an idea; if you want to join in threads on the S&B board, do that and argue the toss if someone says something you disagree with. If you miss certain sorts of threads from the good old days, you could start similar threads yourself. That's more or less how it goes.
It isn't the usual thing, to appear on a board after years away, and saying (now I'm going to quote, as don't want to be accused of misinterpreting op's meaning);
I've been having migrating over to here again recently after a long time away and it's all Roman Originals, granny sandals and things that "wash well".
WTF happened?
The things I've seen on here over the past few years are just absolutely hideous.
But I'd say in the past it was about 80% style, 20% dross and now it's more the other way round.
Was there any need for an entire thread on this really? Especially since the concensus seems to be that there is room for everyone (even people who like Roman Originals). Nobody is going to curate the threads so that it is more fashion focussed.