I think the difference is often in personality type and why you quilt. Some people enjoy the process--the quilting, sewing, planning, cutting, etc. is what we/they enjoy.
Others enjoy the finished product and their goal is just to finish--they may or may not enjoy the process-but probably do or they wouldn't do it, but without finishing the project, it is stressful. They are project-oriented and have the need to finish.
Just like my son love to play with Legos and seldom seems to finish building things, I think I enjoy working with fabric. On the other hand, i do finish quite a lot, but I understand better those who just love to sew and start things. It is less of a "sign of an undisciplined person" that you have so many started projects, but rather, that you love the process--at least the part of deciding on colors, cutting, etc.
My husband is the same way about projects around the house. I counted up several--working on a bathroom, a deck, and now a quilting frame (for me). Eventually he will probably finish all of them but he doesn't feel the pressure to finish them all before he started a new one. I used to get impatient with him about it, but then realized he just likes to have a project going and doesn't always feel like doing the same thing.
That's my story and I'm sticking to it!