productivity went up

I suspect this is partially a result of change, not that work from home was implemented. Shaking up a work environment (for something more desirable to the employee) is always a morale and productivity boost. Move everyone from a bull pen to offices, or move to a new facility where there are fewer distractions and new equipment, or simply change the work schedule to a 9x9 or 4x10 and you'll see short term gains. .

Regardless of the cause of the productivity boost, full time WFH will come at the expense of training young (or new to the field) employees. Ironically, part of the cost of training new employees comes out of the billable hours of the experienced ones. I wouldn't be surprised to see a 20%-25% reduction in output of an employee who is given an intern or new hire to mentor. That won't happen when you're remote because the new hire can't constantly bug you for simple requests, ask for more work, or require active review and monitoring of their work process. But in a couple of years, you'll have two people at 100% (nominal) output in return for the loss in productivity of the mentor.

It's said that it takes 150% of the annual salary in costs to a company to replace someone. Having mentored young engineers, most cost me far more in the first year than I billed, and it took close to 3 years to break even - and that's at a relatively low salary. To have mentored someone remotely for the first year would have likely taken even longer to get them up to speed and profitable. In the short term, moving your office of independently competent individuals remote should absolutely produce a boost in productivity.

Anyway, it's this long view that is the actual, actionably logic behind the return to the office. That isn't to excuse the micromanagers who's only job was to walk around and remind people to put covers on their TPS reports - they are no more than overpaid hall monitors and a relic that should die. It also doesn't excuse the upper managers who never understood the concept of sunk cost in college and feel that they need to fill the seats in the building where they have another 8 years on their lease.