Have O-rings fallen out of fashion?

Internally dampened switches are much more common now, so that's one thing.

QMX Clips present an interesting but underrated alternative, probably hampered by poor availability.

People do use o-rings. You just don't hear about it, because (a) the topic has been covered for a long time so there isn't much new to say, probably; and (b) the people that use them don't post much, I think even some vendors (still) ship keyboards with o-rings installed from factory. I have recently traded some keyboards through local classifieds and randomly stumbled upon keyboards with added o-rings and perhaps replaced keycaps (e.g., Cooler Master board w/ MX Brown, o-rings and a Leopold PBT set).

/r/MechanicalKeyboards Thread