How is this UX behaviour a special case? HSTS also requires the brickwall UX, so does the OpenSSH key change scenario.
The original sin the Browsers had is that the initial SSL UI was built by people who had no security UX background because almost nobody had any security UX background. This was the era when PGP was considered usable security technology.
So when HCI studies start being done (e.g. at Microsoft) and they come back with the scary result that real users just perceive TLS error dialogs and interstitials as noise to be skipped, there is a problem. Lots of real world systems depend upon skipping these errors. I worked for a large Credit Reference Agency which had an install of Splunk, but for whatever insane reason it was issued a cert for like 'splnkserver.internal' and the only HTTP host name that it accepted was 'splunkserver.internal'. So every single user of that log service had to skip an interstitial saying the name doesn't match. For years. Probably still happens today.
Browsers couldn't just say "OK, that was bad, flag day, now all TLS errors are unskippable" because of the terrible user experience induced, so what happened instead is a gradual shift, one step at a time, from what we know was a bad idea, to what we think is a better idea. That means e.g. "Not Secure" messages in the main browser UI replacing some interstitials, and brick walls ("unskippable errors") in other places where we're sure users shouldn't be seeing this unless they're being attacked.
HPKP was new, so like HSTS it does not get grandfathered into the "skippable because this is already so abused we can't salvage it" state. If you went back and asked HPKP designers "Should we do this, but with skippable UI?" they would have been unequivocal, "No, that's pointless". HPKP and HSTS only improve security if the users don't just ignore them, and the only way we've found to make the user actually pay any attention is to make the error unskippable.
Yes that means "badidea" and subsequent magic phrases in Chrome were, as they say themselves, a bad idea. Because users who know them just skip the unskippable errors and end up back in the same bad place.