I've got to imagine that some of their revenue losses in advertising are due to the fact that various companies/brands simply don't want to be associated with Musk in the slightest. If he was serious about ad revenue, he'd also be serious about Twitter's branding.

Note that I'm not saying there are no Musk fans in the world - there are. But he is divisive, which is a trait not beneficial when trying to strengthen your brand.