I don't people are understanding this very well. They hear vaccinated people can spread the virus and think they're as much of the problem or are spreading it to the same extent as the unvaccinated. The part of the CDC announcement stating that vaccinated people passing along the virus is a rare event is not getting through - you really have to go to the original source material for some of this.
The sticky wicket is the same problems as earlier in the pandemic: Rare means little, if all it takes is one to set off a new transmission chain. A vaccinated person is unaware of the moment when they are highly contagious. Without clarity on that key piece of information, people need to be mindful that any given moment they might be. Which is why we're back to masks. We don't know when or who.
There was a Twitter thread about Germany, where rapid tests are so cheap and available, that people take one before they gather, enter an amusement park, and kids are tested in schools twice a week. If vaccinated people could find out they were technically positive and likely infectious, as easily as we take a temperature or pregnancy test, that would be a "not-mask" tool that would be effective at diminishing the chance of spread. Assuming, people who got positive tests would actually isolate or mask for a few days, and not do the "I don't feel sick, so I'm going to go to this birthday party anyway." Which in the US, is a big assumption.
Instead, the only way vaccinated people know, is if they get tested like athletes (rare) or are sick enough to feel like they are willing to deal with a testing site, which means they've already been spreading it around (too late), or they're buying them 2/$20 from drug stores (not cheap, so not highly / frequently used). People are so resistant to every part of this, we went all in with the best bang for our buck... vaccines, and everything else fell away. Plus, there is no profit in cheap, rapid testing. Worse, if people can't even comprehend there is a need.