I always feel there's a bit of a case of exaggerated expectations for RPing (and creative pursuits in general).
You have to ask yourself, "what does success mean for me as a GM/RPer"?
And realistically, if success for you is a several year long RP that runs perfectly, you will always be disappointed. Even expecting more than two people to post their interest or even commit to an RP is a pretty lofty goal.
RPing is like any form of writing (although I don't really think it's exactly the same as novel writing) in that it takes a lot of work, practice, and failure to learn. And like life, it's doomed to die. You can never beat death. Your RP no matter how great, no matter how fun, no matter how much effort you put into it will die (but you should embrace that and it be a motivating factor).
Reasonable goals when you start (or as you learn) are things like "I want to get 1-3 posts in before this RP dies" (as a player or GM). Looking at all the RPs posted on this forum, if you manage to make one post as a player or get one player post in your RP, then congrats, you've now reached the elite of the elite in terms of RPs, players, and GMs.
Eventually you might find groups or individual players you jam with. This however rare, this is special, and it isn't something you should expect to find regularly (e.g., if you are going into RPing expecting to find your creative soul mate or best friends for life, then you are setting yourself up for failure). If you do find people that you mesh with, then at that point just enjoy it for however long it lasts (there are no assurances of time in RPing or life).
RPing is a fun, ethereal hobby you should engage in purely for your own amusement, chasing success (outside of your own fun and the fun of other people) or "popularity" is massive waste of time in a medium that amounts to "I put on my wizard hat".