If you are a massive company, by allowing full remote you could be saving hundreds of millions of dollars on real estate, office upkeep, electricity, etc. You can recruit employees from all over the country so your access to talent is superior and you can afford to pay talent less.
These benefits are easy to analyze, it's just a massive amount of money and time being saved.
Now to go to the less tangible benefits that don't necessarily positively impact the business itself, employees can live in cheaper cost of living areas and actually have the ability to one day own property. Massive reductions in carbon emissions because of 0 commute. Massive time savings for employees because of 0 commute that they can then use to spend more time with family or friends, exercise, or sleep more (all of which could lead to healthier employees). Oh, and they will actually be able to live close to family since they will not need to move to a different state / city. There will be much more efficient use of space, office space is basically redundant when employees can work from home. This freed up space could be used for housing which we desperately need. I'm sure I could come up with a million more benefits of wfh.
To advocate for return to office you need to make all these logical leaps that somehow being together in person will result in us making more money than what we save from being remote and is better for employees somehow.