> Look at what has happened with misbehaving CAs.
OK. Perhaps you have some examples in mind?
> The responses have ranged between nothing and removing them 5 years later.
Certainly you've got an example of "nothing" and of "removing them 5 years later" to start with, right?
DigiNotar is the most obvious example of a "misbehaving CA" that you might be concerned about. In June 2011 their services were broken into and they decided not to tell anybody. There were no technologies in place at that time which could detect problems like this without DigiNotar's assistance. At the end of August a google.com certificate issued this way was used to attack Iranian web users, but Google's Chrome browser had pinning protection (only for Google's own services) and so at this point it detected the attack in progress.
Mozilla shipped updated Firefox versions which distrusted DigiNotar's public root in about 48 hours (not "5 years") and over subsequent days distrusted the entire DigiNotar hierarchy including those parts the Dutch national government had insisted were fine (they were not fine).
The public reactions at the time mirror your incredulity by the way, people who grep'd their newly updated Firefox and discovered DigiNotar's CA certificate (in fact blacklisted explicitly) as "proof" of a conspiracy by Mozilla to send all their traffic to some scary foreign company.
Perhaps DigiNotar just isn't recent enough for you. So let's look at rather smaller deviations from the more recent past. In 2015 WoSign (a QiHoo 360 company which operated a CA) acquired the Israeli CA StartCom in secret. No significant countries have any mechanism in place to detect this (a potentially hostile acquisition of a private company) and so the browser vendors had no idea until mid-2016.
Not telling Mozilla about this was already a violation of both agreements (for WoSign and for StartCom). But in 2016 WoSign/ StartCom (now one shared controlling mind) minted new certificates using SHA-1 signatures for several outfits, notably an Australian financial services company named Tyro. Since new SHA-1 certificates were prohibited in browsers in 2016 these certificates were back-dated to appear they'd been issued in 2015, another violation of the rules. The Tyro cert was probably actually issued in June 2016.
After conducting an investigation which included having Israeli documents assessed by a Hebrew-speaking lawyer and a bunch of digital forensics work, by September of that year Mozilla was instituting partial distrust of WoSign and StartCom, and in 2017 the browser distrusted them entirely. Other vendors followed suit (very belatedly in the case of Microsoft).