When the authors cannot rely on players having background knowledge and expectations built up from exposure to other media, they have to do a lot more work. On the other hand, there are also much greater opportunities for developing the story when the authors have this much control. Without genre-defined preconceptions the instant recognition is lost, but so are the constraints that so often result in cardboard characters going through the motions. One reason is to explore a variety of viewpoints on the same situation. It is easy to see why few allow you to choose your character.
Text adventures depend heavily on description and interaction for their atmosphere.
There would be little benefit in having multiple PCs unless those characters were well defined, and their interactions with NPCs suitably varied. This requires enormous effort on the part of a game's authors if the different characters are interacting with the same people and places, since NPCs need different responses for each, and ideally location and object descriptions would vary slightly too. This argument would not apply to a text version of DOTT, however. There the characters are in distinct settings, interacting with different NPCs, so it would merely mean writing the three sections of the game in differing styles. I still think there is scope for further experiments with multiple PCs.