[stefan_]

It cuts both ways - when 5GHz was new, there were lots of client devices that didn't support the DFS channels at all (even if as stations they don't need to do DFS).

So still today AP vendors are cautious to use them because of the potential for support calls from people with older mobile devices that "don't show the AP at all".

[dboreham]

This can even happen on 2.4GHz with the extra channel allowed in Japan. Stations and AP can disagree about whether they're in Japan.

[stefan_]

2.4GHz channels are another of the many many regrettable paper cut things with WiFi. I have a 2.4 only gadget that the manufacturer ships with the narrowest regulatory settings so they can sell one SKU and it can't use channel 12 that is available almost everywhere but the US.