I don't know why everyone else practises, but I began with the intention of integrating my body into the rest of my life.
I am not as hyperactive now as I was 20 years ago, or even 10 years ago, and maybe I'll mellow further with time till the moss covers me over in the corner of the garden.
You know what I mean?
I know what you mean, at least in part.
I started training because I felt I needed a self-defense option that was between running away, and shooting my attacker. I chose aikido specifically because I was intrigued by its seemingly unique approach to "fights." No more punching and kicking for me!
After starting to train, reading a lot about aikido, and really getting into it, I realized that there's a lot more to this art than I first realized. I've been training for almost seven years now (a drop in the bucket, I've also come to realize), and I'm quite a bit mellower than I was when I started. That could just be age, but it's probably partially due to my training.
In the back of my mind, though, is still the goal of having an effect response to violence. That helps keep me focused and grounded in reality (as I perceive it, anyway).
I don't know how I'll feel about training after another 13 years, and I'm not sure I'm any help. I do know that I have on occasion had to care a bit less or be a bit more selfish about the dojo and my training. Detaching from the culture of the dojo and just focusing on what I can do has helped me get back on track when I get too involved.