That's exactly what happened to me. I played it obsessively for a few weeks and then it just started feeling like I was solving the same kind of problems I already solve all day for money, and if I was going to be doing that I might as well be getting paid. Which I guess shows how much I love my job (or at least the fun bits of it) but also kind of took the wind out of my sails in-game.

Edit: Also I got to the endgame point where you spend 99% of your time just setting up new mines and rail depots to keep feeding the beast. That was a fair while ago though so maybe there's more to do endgame, or maybe I'd just finished the game which is also OK.