London's Drive to Work Day

OK, in brief, if all of us who cycle started to drive to work, or even take public transport, we would see those systems start to fail, as the pressure on them increased.

and this^...

And also playing with the philosophical contrast between a drive to work day as opposed to a cycle to work day. People who drive are not evangelistic about encouraging other people to drive whereas many people who cycle wish others to do so too.
Now why is that?