Because the roads then fill up with commuters that come in from even further away. Imagine your typical city - jobs in the centre, housing on the outskirts, everyone doing the rush hour thing. People might be prepared to give up three hours of their day for the required commute.
Now if a magic wand is waved and people start to work at home then those desks in the city centre will still be there. If the roads are that bit - 10% - faster/clearer then that tempts people from neighbouring towns to commute into the big city as they can now afford the time to do so due to the roads being quicker.
Rather than work remote the far better idea is to have people work local.
Imagine you have a programming gig on the other side of town and commute across town taking an hour or so each way. Coming the opposite way is someone else who lives near where you work and they are trying to get to an office down the road from where you live. They are a programmer too.
Now what if you could swap jobs with them? In that way you might have a ten minute commute and they might too. In that way a far bigger difference can be made. But the thing is that we don't have a means of matching these job swap opportunities up.
I dunno, you're pinning your dismissal of the initial idea on 'those desks in the city centre will still be there' when it's entirely feasible they'll just reduce over time in-line with demand. In fact, we see that right now with the trend towards unallocated desking and flexible working, where desk numbers within the same floor space is being reduced in favour of deploying more collaboration spaces and allowing more staff to work away from the office in a manner than suits them. That's what that reduction in office density downtown looks like in practice.
Then your counter proposal depends on people being able to 'swap jobs' while handwaving away the complexity that would involve. Most knowledge worker roles aren't that fungible.
Now if a magic wand is waved and people start to work at home then those desks in the city centre will still be there. If the roads are that bit - 10% - faster/clearer then that tempts people from neighbouring towns to commute into the big city as they can now afford the time to do so due to the roads being quicker.
Rather than work remote the far better idea is to have people work local.
Imagine you have a programming gig on the other side of town and commute across town taking an hour or so each way. Coming the opposite way is someone else who lives near where you work and they are trying to get to an office down the road from where you live. They are a programmer too.
Now what if you could swap jobs with them? In that way you might have a ten minute commute and they might too. In that way a far bigger difference can be made. But the thing is that we don't have a means of matching these job swap opportunities up.
Time for a YC job swap for lazy commute startup?