Your parents had nothing better to do in February. 
My grandpa was the oldest son of NINETEEN kids.
The explanations I was told:
My great grandpa had 6000 acres and needed farm hands
No TV in the 1910's
Too poor and too rural for radio
Too lazy to build up the fire
Not enough blankets
Didn't learn to read until after kid #14
Didn't like reading until after kid #18
and my favorite:
oops...