Doctor Who

Same reason why he never went back to Ruby Road to find out Ruby's mother's identity: he'd already been there once.

My understanding is that, as the Doctor had already been there on the 23rd (tracking down Belinda after Conrad told him about her), he didn't want to cross his own timestream if he could possibly avoid it, and preferred to arrive after his past self had left. Yes, you CAN cross your own timestream, as many crossover specials have shown, but the Doctor considers it an unnecessary risk when the vindicator option is available.