Keep in mind, these are all just my own personal opinions.

Echoing /u/cyalith, yes it can take a very long time for some scripts to be done. I know some writers who have scripts that have never been done, that are 6 months, a year, or longer, old. Not everyone likes to do scripts, and those that do don't always dig deep to find them and sometimes tend to do what's immediately offered. I think people have their own, sometimes complicated, reasons for choosing what they do.

Also, if a script is done by someone seen as super popular and gets a ton of upvotes certain people may then shy away from it for awhile. I know some (me? most?) performers do not like the idea of being compared to someone else, again, this is just my opinion.

As for your last point, if you want a specific person to do your script, which sort of sounds like what you're asking but I could be wrong, the best way to go about it would be to PM them and maybe politely say that you've written something you'd like to offer them, and would they be interested in reading it? Would be the...least invasive way of going about that.