The question is not whether they can find someone else to hire. They can always do that for the prevailing market price. The question is, how much more do they have to pay to get someone to take on ~$30,000/year in commuting costs than they would if they didn't require that?

You are so fixated on costs that literally do not matter to an organization that can fill an in office job at the rate they want to pay.

The rate they want to pay is "less".

Doesn’t matter if someone will accept it and work in the office. That’s what the value the job is worth to both the employer and the employee.

I feel like you're still not...

So suppose the employer's benefit from having the employee is $150,000 if they work from the office and $140,000 if they work from home. Meanwhile the employee would accept $130,000 if they had to work from the office or $100,000 if they can work from home.

You're saying, $150,000 is more than $130,000 so the employer can pay them $130,000 to work from the office and everything's fine.

But the difference between $150,000 and $130,000 is less than the difference between $140,000 and $100,000. By quite a lot. So why isn't the employer going to want any of that money?