Just ask yourself the same question in regards to whatever it is you like to do. Motivations can come from anywhere, regardless of if it's freeriding, rails, kickers, or any other aspect of any sport - wanting to do something you saw someone else do, wanting to be better than someone else, or wanting to be better than you already are. For me it's about competing with friends and just improving personally. I don't get a specific buzz out of rails, I think it's just easier to gauge progression in the park than it is in big mountain freeride. I have just started doing rails and for me it just seems to be the next thing to do to progress. i mean the park is really just a simulation of things that you may find when you are snowboarding. sometimes in the quest to get from A to B you need to jump over something or slide across something. having park skills certainly does improve your natural mountain riding. I don't really do rails, but I do boxes. I think I have the skills to do a few rails, but not the skills to do those rails with 100% success rate, so I mostly opt out. The consequences of screwing up can be so gnarly and I feel like I'm too old (at 30) to get able to easily get up from stacks and keep riding. I'd prefer to just progress in tiny increments and keep myself as safe as