I have considered this before and I know others have too, but the amount of work involved in getting a playable 1 person story style map is enormous compared to the payoff.
If it was to be any significant length, it would need to have a LOT of content, which has previously not worked very well; take RandomDungeon as an example.
An amazing map made by Vesanus who is by far a much more skilled creator than me. When the bot count increases, the map tends to suffer and become unplayable, especially when higher pings are involved. This is no fault of Vesanus, and is more a product of how chiv isn't really designed as a single player, story driven game. Which is also more to the point. Though this might be fun for a few playthroughs, the game is designed to be played with others. I know personally that when I design a map, I spend stupid amounts of time obsessing over things like the placement of carts, or is the grass looks suitable for the terrain. It would break my heart if people only played it a few times before getting bored.

Probably not the answer you were looking for, but this is my take on why there arnt more single player style maps out there. If you were interested in different experiences, I would lookup Stronghold (also made by Vesanus), all the different flavors of horde maps / infection modes, or even chivball (shilling my own map, i know).