> For example, if Elon suddenly starts sharing pictures of himself giving a nazi salute and promoting holocaust denial, most brands won’t want to be associated with that.
Brands can back out if and when that happens, no need to do it preemptively. And besides, an advertiser is not a business partner: there is no exclusive association between the brand and the advertisement outlet. Your next example shows the difference:
> See also: Kanye
Kanye is a business partner of the brands that sponsor him- they use his image to promote theirs. It makes perfect sense for them to stop their partnerships when his image is tarnished. But brands don't use Twitter's image to promote themselves, they just rent space to reach its users' eyeballs.
> he named and shamed those brands with the implied threat of boycotts...
No he didn't (threatened to, never actually did it afaik); but how come that brands are afraid of vague risks for the future of a platform they simply advertise on, and not with the much more credible risk of being boycotted by a few million customers who also happen to be Musk's fans?