Again this heavily depends on your situation.

I live a 20 min walk from my office. I have £0 commuting costs.

On the other hand I live in an old city with little new built housing. My flat is over 100 years old with massive ceilings, electric heating and no way to way to improve the insulation. Heating it just in the evenings for 5 hours costs about £50 a month, heating it while I work will likely cost £70-100 extra in top.

It’s not a zero cost: it’s 40 minutes of time.

I run there, which is time I still spend at home. And I enjoy the walk home as I live in a beautiful city. I normally go walking throughout the day for longer than that anyway.

Yes, I love being able to walk/bike to work, but that’s not life for 95%+ of people in the US (nor England from what I know).

Walking/biking gives you agency that public transit/cars don’t. It feels much freer.

Biking in Tokyo is less freeing than public transportation because of the added time finding a place to lock up the bike. I bought a bike thinking I'd use it but it turns out it's actually much less free since if I take it I'm stuck with it the entire day where as without it I can easily visit the other side of the city on a whim via public transportation. The same would be true in Singapore, Hong Kong, Paris, Berlin, many other places with good public transportation.

You should look at getting a folding bike. I got a Brompton recently, using a company cycle-to-work scheme and it's been brilliant. I can cycle 3-4 miles in 20 mins to my favourite coffee shop, fold up my bike in 20 seconds and stash it under my table.

It might be a net positive if they enjoy the walk more than 40 minutes of other activity.

WFH doesn't mean they can't walk for 40 minutes though.

But in the context of office vs home, if the OP is basically saying "I like my free commute" then you have to remove cost & time from the "pro" list for WFH.

I used to like reading on the train as time for myself but it didn't balance out the other stress & cost of commuting.

If Transport for London said that trains would be free at the point of use & actually put on enough service that most people got a seat I'd definitely consider the office more favourably again

Not to mention the infrastructure / tax costs! New interstate lanes to sate population growth don't build themselves.

The more regular commuters we can take off the road, the better.

Some of my transit activist friends are upset over the potential of work from home to harm demand for transit service, which for some populations are used for more than commuting to work. Also if more people end up moving out of city centers because they're no longer constrained by a commute, that further erodes the demand for public transportation.