You might be inclined to move home to be within walking distance of your office, or to work from home sometimes, or to use the (very good) Velib bike hire scheme, or buy a bicycle or a motor scooter.

Metro rail is sexy, but it's only one part of the transport mix.

I move about almost exclusively by bike, but I realize that for many people it's not possible to live close enough to their workplace to do that comfortably. Also, Paris is a terrible city for cyclists (at least that's what it looks like in the videos I've seen) and it takes decades for infrastructure to be built up sufficiently for people to feel safe on a bike.

I think that making public transport free in an easy step on the way to a city that relies a lot less on cars. Of course making it more attractive to walk or cycle and more expensive to drive is very important too, but that requires a lot more work.

biking in Paris is worse than you think :

it’s dangerous because roads are very narrow ( so protected bike lanes are rare) and there’s a lot of traffic.

the bike city service got changed recently to include electric bikes and as a result nothing worked for months ( not sure it’s back to normal yet).

Even if you manage to get a bike there’s a very high chance your bike will have defects because people like to do stupid things with them, like getting down stairs, or hitting the curbs.

and finally, if you think about buying yourself a bike, expect to have it stolen on average once a year ( depending on its price).

"You might be inclined to move home to be within walking distance of your office"

Very few people would have this luxury in city like Paris, where housing is prohibitely expensive in the city center, where many offices are traditionally located.

And, before you say "You might be inclined to find a job where more affordable housing is available", many people do not have so much choice in terms of where to work (same as working from home).