A subway is only for local trips. And only a very small part of the world has subways. I have never lived in a place with a subway. I did briefly live in Amsterdam but the subway wasn't very useful there.
With private transport I can go anywhere on the continent whenever I want.
Edit: reply to flexagoon since I am rate limited:
Going around Europe on trains is a total pain. There is a reason almost nobody does that and use airplanes instead.
Perhaps they can make the comfort of trains comparable with airplanes, so more people use it.
I'm OK with allocating tax money for better public transport but I just don't see myself using it.
Of course, I don't think anyone in this thread is advocating for banning private transport and only keeping public transit for everything. But most of the trips people take are local, and a good public transport system makes that much better for everyone (including the car drivers).
You can also go around the continent on trains. We should have more high speed rail.
Private transport is of course still hugely useful for many cases, but there are also many cases where it could easily be replaced for many people by a good transit system. And I'm not just talking about the US, which people usually give as an example of bad transit. EU's railway network should be much better.