Hunter:
Okay, let me see if I can explain this. I'll pick on a theme I've used before with some success: High technology people trapped in a low technology world; something like Traveler characters in a D&D world. The concept itself is straightforward enough; but I'm running into "what do I do after they get on the planet" and "how do I advance the story along" once they get there.
I just noticed this from before, I somehow missed it back then...
You don't have "ideas", you have "idea". You either need more than one idea or you need Players who will sandbox the hell out of your "one good idea" and generate their own content... and those Players are few and far between on Play-by-Post
[1]. Also, I just read your Game Information pages from all the games of your I could find, around 6 of them. All but two were very "epic quest" orientated and that doesn't lend itself to sandboxing. My suggestion?
Work out the intro and ending at the very least, or the ending you "kinda hope the Players will aim for". If you can get those two ideas hammered out, I find the rest starts to fall together as PCs interact with you intro and the bread crumbs of the ending you deploy.
And by intro I don't just mean "High tech characters crashland on D&D world". That's a
premise. I mean "and what happens next?" Like they crash, but then do you have the first three-to-infinity encounters planned out? Do they crash in the middle of Lizard man swamps and make friends? Orc territory to be hunted as prey? In the middle of the Elf nation to be Poncy-Elfed at? In a remote area where it'll be months of hard scrabble survival before they meet anyone and have to contend with the native wildlife and magical and such beasts?
That's your intro.
As for ending, even in a "The
Minnow would be lost" pure sandbox scenario... to what end? What are you
hoping the PCs will get up to? Build a high-tech haven on this benighted magical backwater ala almost every fantasy author ever? Integrate? Become world leaders? Defeat the ancient Evil using their high-technology Swiss Army light-sabers? Even in a pure sandbox, you need something going on in the backdrop for the PCs to either interact with or ignore or co-opt as their own. If you have nothing... the Players won't do all the work for you.
So yeah, maybe hang up your hat for a bit and work on those ideas. Hammer out some campaign blueprints, beginning and middle/end, and then come back at it. Or do what I'm doing right now by accident, find another GM who has those High Concept beginning, middle, and end parts and help them (or have them help you) and
run the rest of the game.
1 - Yes, yes, we're all perfectly individual snowflake Players who can on a whim come up with all the sandbox content a GM could ever want... except no, we really aren't and it's a two way interaction. Players need a GM tossing out ideas and wrinkles to the Player's plans, and GMs need Players who generate their own plans and find a 3rd option to the GM's planned out scenario. And then all the filler Players to fluff out the team with, we perfect snowflakes know what I'm talking about; the murder-hobos, the coattail riders, the sheep, the cats, the dogs, the makeweights...