I am, and many other designers are as well. With HDR monitors becoming more popular, more and more gamers are now using such monitors, too.

The distance in quality between a typical prosumer (be it gamer or designer) panel and a common cheap panel is increasing significantly.

Asus, Apple and Dell are the companies at the forefront of this change, while other companies still sell 6-bit monitors that don't even reach 70% sRGB (~85% of the current market don't have 8-bit/300 nits/95% sRGB)

I do have a "HDR" monitor, but as far as I know most gaming HDR monitors don't have true HDR, and usually have a peak brightness of 250nits (or 400-500 nits for the more expensive ones).

Also, I am on Windows, and HDR is unusable on Windows in normal usage, and very few games/applications actually support HDR.

I understand that some enthusiast monitors do exist that might reach 1000 nits and are actually used in HDR mode, but I think that those users are way under 1% (even 0.1%) of the traffic for the most websites.

That's the point I was trying to make: those extremely high-quality monitors are basically ~0% of users, but a significant percentage of creators. And creators often design stuff so it looks great on their own displays.