The number one reason for my loss of interest in other hobbies is focussing on my young family, and my career, both of which are fulfilling for me.
As far as hobbies go I find that only one fulfills me now and it comes in two seasons, Hunting Season and Getting Ready for Hunting Season...
I used to be an avid fly-fisherman, loved baseball and beer league softball, enjoyed skiing and snowboarding, wake boarding and drinking beer on the lake, etc. Now I hunt, or prepare for hunts. I also used to LIVE for waterfowl, especially snow geese, and pretty much spent all my time hunting birds, even went 11 years without a big game hunt, but have now switched priority to hunting as many big game hunts with my bow as I can. I still love the challenge of decoying birds in close, but find bowhunting the ultimate challenge I've been looking for...