Been shooting since I was a kid, but never had much interest in BP. My interest later in life has been in modern firearms. I have a business that caters to the AK, AR, and other semi auto rifles and carbines.
My son got interested in hunting, so we took him through the process. Finding out about muzzleloader seasons was the impetus for us, plus I've thought the "traditional" rifles were beautiful. Local gun store has one for sale, we bought it for hunting. I then decided I should have a BP handgun for carry while hunting ML season. That's all there is to it. Got hooked from there.
I'd stop far short of calling it a "lifestyle" though. When I take newbies to the range, we use modern "tactical ninja" weapons all the way through to BP. They like the opportunity to learn a little bit about several types of firearms. Plus I can say, "See this-- this was in the movie, The Kingdom, and over here, this 1858 Remington NMA was in the movie, Pale Rider." And so on. You can see the lights coming on in their heads. The curiosity has been there because they've seen some of this stuff, but they've never known anything about it until now, when they actually try them in live fire, see how they work, and see what they can do.