It keeps me off the streets and out of trouble!
It also keeps my brain working and stretches my creativity. Quilting allows me to express that creativity more than most other activities. I'm not the best "piecer" or quilter around, but it is fun and mentally challenging.
I chose quilting partly because I am 'geometrically challenged' and color impaired. The color part can't be improved - it's the way I was born - but the geometry involved in piecing quilt tops is gradually getting easier. Since I am naturally analytical and logical, it also makes great use of those qualities, though I do have my share of the "what was I thinking" moments! (Most are related to the geometry thing!)
Note that I am also one of those crazy people who chooses to do things that are difficult for them to stretch my brain! My motto is "Everything is easy once you know how!"