Average people tend to use what they have, I have zero "average" friend trying to get more supported features than there currently are.
And, by the way, most of my friends do not use html/CSS directly, or even indirectly use it besides some bold, coloring or the random photo attachment. Zero of them know caniemail.com, and, if they understood the point of it, zero of them would want or need it.
Average people seeing html in their mail doesn't mean they have an opinion on it, or would want more of it if they were told honestly what it does and who abuses it.
- A normative one : the less is supported, the better.
- A descriptive one : many (not indicative of any share) of their relations actually do that.
None of the points is telling about their relations, aside from, maybe, not having many friends in adtech.