That's basically my answer, every time - until I get into the WHY, for me personally. I took my open water class in May 2013. Went river diving as much as possible between then and March 2014, which was my first trip to Ginnie Springs. The first couple dives that day, I was offered a "guided" dive in the ballroom by my full cave friend and turned him down, but eventually caved (ha) and checked it out... that's all it took. I've literally never dove in salt water at all, just springs, caverns, and caves.
That summer/fall I did AOW, in March 2015 I started cavern. March 2016 I finished cavern (weather/river level issues, work obligations for myself and instructor, family issues, etc. all played a part, but I just kept practicing during that year until I came back and sailed through the last part of it). September 2016 I took intro class. Starting full here in the next few months.
For me, cave diving makes the most financial sense (in addition to being interesting from a science/nature standpoint, as well as just plain fun to plan and execute the dives). The initial equipment investment is higher than what I would have spent on ocean diving had I not started down a tech path... but there is no way in hell I could drive two hours, pay $30 (at most, if I dove Ginnie) and dive all I want, all day long off a boat. Two single tank dives for $60 or more after a 3-5 hour drive, plus tip, and the hassle of actually having to clean gear... no thanks. lol