I just get way too into things I like. I couldn't afford to collect mechanical watches if I tried or at the very least wouldn't want to afford it. But overall G-Shocks fit my style much better most of the time anyway and it's fairly easy to justify getting yet another watch when they are far, far below a thousand bucks a piece.
Comparing my G-Shock "collection" to what I've got in knives and pipes it's a downright cheap collection but brings me just as much joy. It's not even like I've got loads of money anyway. I just never spent a lot of money on many things other people do and always steered clear of debt. Besides the mentioned hobbies I've only ever spent a lot of money on my car and my apartment. Also the only things I've ever taken a bank loan out for.
So it's a combination out of affordability and me just plain liking them more than most other watches. I can only think of two mechanical watches I'd like to get but easily a dozen G-Shocks.