a) Why did you take up cycling originally?
As a kid? Basically because it was faster than walking, more gentle than running... and I couldn't drive. When I grew up, I discovered that I could do almost anything I wanted on a bicycle and that I didn't really need a car... or that I needed one only some time.
b) Why do you still cycle nowadays?
Up until 4 years ago, because it is a fun way to relax and a very nice way to see the scenery. Sometimes, it was also a more convenient way to go shopping than by car (parking problems) or by foot (food too heavy).
Then later with one child in daycare, and now in school, it is a faster and more convenient way to commute, so I added up bicycle commuting. But although I like it – and it is much better than driving –, if I had unlimited time, I would rather walk 8-9 times out of 10 and take the bus once or twice a week.