That's inherent to play-by-post, in my experience. It takes days (sometimes even weeks) to recruit players, submit character sheets, review, revise & accept them and then to finally begin. It's something that people do in their free time in between the rest of their daily activities. Pen-and-paper roleplays have everyone gathered in the same place and that's all people on focus on for hours on end so naturally the game moves faster.
But thank you for your feedback, regardless. I'm slowly starting to think that the "Play Your Avatar" game (which requires no setup time) could be a very good idea to let people jump straight into roleplaying as soon as they join.