They are on posters all over. Commonly used for sign-ups and event entrance. It’s a mid assumption to think they are more popular in tech circles, I actually think the reverse is true.
It's only in markets that lack competition that a company can do unpopular changes that reduce its costs without losing customers. For example, stadiums all went cashless "for your safety" and then never brought cash back. Which they can do for the same reason they can charge $5 or more for a bottle of water: they're basically a monopoly with a large captive audience.
I went to a place recently where you ordered on your phone and it kept your tab open until you closed it... I had to race against my phone dying to pay.
I see QR codes everywhere too. But I never see them used , and nobody in my circle uses them. And the only times I hear about them is when people complain about them in Restaurants etc.
May very well be different in other locations (I'm in small town in Canada, just outside of Toronto, traveling to Ottawa frequently). I would guess without any evidence that downtown NY or Boston may see more use :).
Similarly for restaurants - in my area, while there temporarily were big a few years ago - I don't really see any place that uses them now. The exception is when I travel to other cities.
The number 1 reason I don't bother is that, in my experience, they rarely work.
I've used qr codes maybe... 6 times, ever?
With probably 50% success rate before I give up.
I know for a fact that literally nobody else in my in law family of middle class Canadians has ever used a single one.
Anecdata of course, but if we're sharing assumptions... :-)