My earliest memory (the location puts me at 5) was getting a demolition derby model for Easter. My entire childhood is full of model related stuff, from me on my Schwinn with the mowing money in hand to visiting my cousin once a year (he had an airbrush!). I built a model a week and most of my Xmas presents said Mongram on the side. I also drooled over RC stuff, planes and boats, but they were way beyond anything I could afford. I scored a Cox control line Stuka for a birthday present, but all that got me was a perpetually lacerated finger.
Models pushed my interest in history, from watching the World At War on Saturday evenings to going to the newest bad Charleton Heston movie, whether it was Planet of the Apes or Midway. War movies and models, war movies and models.
Then I discovered girls, music, hiking, kayaking, Scuba.
Next thing I know, 20 some odd years were passed and I had a house, wife and kids. No more time or money for the other stuff, every spare moment was either kids or working on the house. Then one day in a train store I came across a 1/72 Tiger I. I stood there as all the memories flooded back in. I built a few Revell 1/72s, found the FSM forum and my jaw dropped in how far the industry has come with PE, etc. Before I knew it, I was all in. Equipment, ref books, kits, RC...
So, back to the original question, I model because it's ingrained in my DNA. It's a side business, a stress relief, an online bar stool and still the absolute best way to spend a rainy (or snowy) Saturday afternoon.