What drives the modders forward?

I have always been intrigued by what makes the modders delve into a game and change what they think needs changing.
Such as the GWX3 mod, what made all of you dedicate so much of your free time to doing what you've done?
I personally really appreciate the longevity that a great mod can bring to a game and it's the reason why PC games have such a long shelf life.
I bought SH3 from steam for £3 on a sale and didn't enjoy it stock but with GWX 3 and other mods it really comes to life. Also with SH4's TMO and Op Monsun mods and now Sh5 and it's growing mod list.
I ask this question because I have a full time career, 2 kids under 4 and a wife and they consume so much of my free time, they leave only a few hours a night to sit at my desk and play some PC games.
I assume not all modders are single with no committments outside of modding so how do you do it?
Yours,
Much appreciated.
Barso.