It is harder to start an original roleplay. Indeed. However it is far from impossible. I've had quite a couple roleplays on this site, of which two finished, another one lasted for over a year and am currently GM'ing one that's well past the one-year mark as well. So it is possible. However, you must understand a few basic concepts about sociology and marketing to get to that point. Coincidentally, one of those concepts was laid out very literally within this thread;
To use your Blood Riders RP as an example again; it says absolutely nowhere "This is what the world looks like now." or "This is what you can do now." or "This is why you should join." Yet, these are the things that excite and inspire people. That is what they get to play with. A history or legend on the other hand, that's just background fluff. There's nothing concrete you can do with background fluff. Silly mistakes like these are why fandom games have such an advantage over 'original' RP's.