I agree with Son, but want to expand on this post because he left the why out:
Steam Train only worked because A. they were horrendous at the game and B. They went out of their way to make jokes and be generally funny while filming. Game Grumps/Steam Train could do a LP of anything any make it entertaining, since that's literally their job. Hardly a fair comparison.
Video LPs of Civ tend to be boring because few try to be entertaining and no one at all edits them. Watching a guy play a game for four hours without cutting anything is bad, watching a guy play a game for four hours without cutting anything and not trying to entertain the viewers while doing so is even worse.
Text based LPs are much more passable since they take far less time to digest for the reader. Still, no one seems to try as hard on Civ 5 S&T to make interesting narratives or generally differentiate their games, and the few that try to be comedic tend to fall flat on their face. The main problem of pure gameplay stories is that there's literally nothing that makes them different from a game I can play myself. A game I can play myself will always be more interesting to me, and thus there is no reason to invest in most Civ 5 S&T. This is not helped because most players have the same goal: win. There's few self imposed challenges, few attempts of screwing around just for the sake of screwing around, and no soul. I can compare this to CKII, whose gameplay only stories tend to be more interesting, since there is no "winning" in that game. It's much easier to tell a story through the mechanics of the game alone. Although it was a narrative story, one of my favorite AARs (same thing as a LP) on the Pdox forums was a Zoroastrian patrician family in one of the merchant republics. Since that is not easily reproducible in a game without modding or severely breaking how the game is intended to play, that would be interesting to read in itself (the fact it was a well-written story in itself was just a bonus).
Now, compare all of that to narrative stories such as Princes of the Universe. When I read that, I'm not reading for the game, I'm reading primarily for the story based on the game. That's something I can't easily reproduce on my own, and therefore can capture my interest. In the same way, as I alluded to above, I don't watch Game Grumps/Steam Train for them playing the game, I watch it for the insane conversations they have while playing the game.
TL;DR: LPs for Civs don't work because there's nothing to them I can't get just by playing the game myself.