Whys?

For some reason I thought we had by-passed the WHY? stage with Mallory because she has been much more quizative with how things work, sequence etc....What happens next..just ask her about our plumbing, where do things in the toilet go? She will tell you down the pipes, to the street, to the plant etc..
Well today on the way home from a dr. apt it started.

We passed a little pickup parked on the side of the road.
M: Why is that truck there?
me: The house they live in does not have a garage.
M. Why did they not build a garage when they built their house?
me: I don't know, maybe there was only room to build a house.
M. Why did daddy build us a garage?
me: because we wanted to park our cars in it.
M: Why?
I think I changed the subject after that.....