One reason I play Hattrick is because I like the cyclical nature of the game. You start with an idea about what kind of team you want to build, then you train long-term (up to 3 years in real life!). While you build, you can test and try to comprehend the aspect of the match simulation that you want to master. I also like the tactical choices you have to make for each match. But the most important component is the community.
Why I stick around in Hattrick? I think it is love :) I mean, everything I can do to help Hattrick to stay as immersive as it is, is very important to me. I was a moderator, a translator, an editor - just because I felt that Hattrick, in a very peculiar way, was mine. Now I'm a National Coach because of the same reason. I think Hattrick is my game. I want to play forever and stay here with my friends.
What I like about the Hattrick community is that there are real people and you don't just compete against the computers. You play against each other, but you can also help each other in the forum and talk about everything.
In HT, my biggest achievement is to be the assistant manager of the U20 national team of Suriname. And of course also, when my dream came true and I reached the third division with my own team!
Some of my Hattrick friends I've known for more than a decade now, which is longer than quite a few of my real-world friendships. You build up trusting relationships with them, and meet people you'd normally never meet. That's also what I really enjoy about the federations in Hattrick - some are really places where you can share your personal stories. A federation in Hattrick was one of the first places where I disclosed I was going to become a father!
I would say the community is the strongest reason I have stayed in Hattrick for so long. The game too of course. After having trained my players and played in the French Division 2 for a while, I started focusing on training international players to help the Moroccan team. Today 80% of the defense of the Atlas Lions was trained by me!