To be perfectly clear, they are mandating employees be vaccinated if they want to physically go in to an office, not to do (or keep) their jobs.
Given that the CDC just admitted that vaccinated people can also spread COVID (by reissuing mask guidance), what is the point of requiring vaccinations?
It affects the balance of propabilities, and that is everything in the current situation.
Shifts in probabilities make the difference between large scale disease (a wave growing exponentially) or not (decaying to zero).
They CDC have always acknowledged that vaccinated people can spread COVID-19 with some probability. There is no "admission" because that's not new. What's changing the advice is new measurements, modeling, social behaviours, vaccination levels (or hesitancy), and the delta variant all update the balance of probabilities.