I think a lot of folks may succumb to a 1-up mentality to become the most knowledgeable, best at something, to keep pursuing that interest to no end. Maybe folks like that just enjoy the pursuit more than the activity.
I suspect that people that become deeply interested in something that their pursuit of it appears all-consuming also end up having that interest be a part of their persona. It defines them.
People approach a hobby like running and maybe they just assume the end-goal is running marathons. They have to have the best running shoes, heart rate monitor, sport watch with GPS, running shorts, special headphones, etc. Maybe you'll enjoy running just one mile in a pair of discount running shoes.
Its ok if you have a different level of interest in a hobby. Maybe you have 5 different hobbies you are interested in and like the dynamic nature of switching to a different hobby when you get a little bored with one.