It seems foolish to rush things as cases are once again back on the rise, which means deaths will likely be rising in about 2 weeks. And why are cases on the rise? Because people are, once again, pretending we are getting back to normal and going back to their old germ transmission daily life. How many times do we need to go through this Grand Opening / Grand Closing cycle before we learn?
I'm guessing they are looking forward to the point at which "everyone that wants a vaccine can get one", at which point safely opening an office building should be doable.
(Fully) Vaccinated people spending time together seems safe enough though, so the choice to work in office is probably fine (whereas requiring it is premature).