> I suspect that people using popular browsers would never even notice that varying the Accept-Encoding header had no effect, and that is why the CDNs believe that this is OK.

I feel like this is a trend for pretty much everything on the internet these days, the 1% of anything doesn't matter to any service, not using google chrome? "please use a supported browser - aka google chrome", using a VPN? CDN level block or "here's 1000 captchas because Google hates you", You want en-gb? not from that IP enjoy your crash course in the native language, You aren't in the USA? no content for you.

Excluding the 1% might make business sense as an optimisation abstractly, but when that 1% could affect different people each day it can affect everyone eventually and you will actually piss off all users.

not only in tech, but also in business practices. I live in Germany and don't speak German. Spotify refuses to send me any communication in English. Amazon Prime refuses to serve me English-language content, and so on. When trying to get my language switched on both I got the stock response of basically "we know this is a problem, but we're not going to fix it because it affects too few people".

It's just a come back of "Best Viewed With Internet Explorer"

It's far worse, back then stuff just rendered a bit weird and looked crappy but for the most part would still actually work (outside of corporate intranets jscript and other M$ only tech was not as widespread on the open web ). The difference is in the message "best viewed" vs "not compatible" vs "infinite captcha loop with americanisms" vs "not available in your country".

Now it's really common for stuff just to straight up not work or you are actively blocked and considered collateral in protection against spam and botnets, the latter is an entirely new phenomenon.