Old habit. I'm a kid of the 1990s, and we were convinced there wasn't anything cooler than a) video games and b) replacing letters with numbers. It retrospect, we might have been a little biased.
Well, just for future reference; if you're a kid of the 90s, you're well into your 30s now.
It's weird/juvenile to be typing a phrase in a manner similar to a preteen, well after 20+ years have passed. Especially in the middle of an otherwise normal message/conversation.
