My motivation is that at the end of the day, these arts are fun. I couldn't keep going if I didn't enjoy them at the most basic level. Learning, teaching, sparring, and writing about these arts are fun in a way that allows me to get exercise, manage stress, and develop effective self defense skills.
The answers to this question are also great. It makes me smile to see so much dedication to students and keeping the arts alive.
My motivation is the skill level that I see in my teachers which I would like to have someday.