You lose money when everyone browsing in incognito/tor/cookie-blocking sessions gets the damned cookie warning every visit, and eventually tires of your site's nagging and goes somewhere else. Or maybe you don't, maybe those users had 17 ad blockers and you don't lose a dime, but it certainly hurts your company's goodwill to have less eyeballs.

If users don't bounce, is that based on short-term or long-term research?

Users don’t behave that way. I don’t care about the incognito dudes. Cookie warnings are so passé that all users have trained themselves to always accept. That’s what my user research shows.

Fears of bounces over cookie warnings are overstated. Users do not care.

If a site I use regularly has an annoying cookie warning, I just use uBlock Origin's element picker to hide it. I wonder how narrow the set of users are who care enough to block cookies but can't easily disable the warning.