Because 42 is the answer to everything.
As decreed by a wise and all-knowing deity.
It's only natural that the answer to the ultimate question would be 42.
It's a number that just works.
It's the number that just makes sense.
Because it's the number of letters in "I am a number".
It's the number of times you need to try to get it right.
It's the number of people who will disagree with you.