Say you work 100% remote, 8 hours a day. That's 2080 work hours a year, out of 8760 hours.
That means you need to be connected to internet, have electricity, etc. 23.74% of the time - let's round that up to 24%
Say a worker pays $600 / year for internet, $2400 for electricity / year, and - dunno - $1500 for your cellphone / year.
So that's $4500 / year, and your employer must cover approximately $1080 of that. If the company has 1000 employees, that's a million in extra costs.
Doesn't really sound like it is going to break the bank, especially not if your employer is also able to cut previous office-related costs.
Also, employers would probably start to offer a bit lower salaries to the workers that don't live in very high cost of living areas...if you pay 1000 employers on average $100k / year, that's a minimum $100m in annual salary expenses. If employees are willing to take a $99k salary for guaranteed 100% remote work, with the above expenses covered, then those costs are offset for the employer...