I think because Amy is part of the Doctor's personal timeline, thus cannot even if it(she) wanted to.
Plus, maybe that _is_ where he needed to go. Think what would have happened without that misadventure. He wouldn't have dropped off Amy and Rory for their own good and gone traveling without them. Instead, he would have spent time with them, and come back and visited them repeatedly, and eventually they'd grow old and die like the Brigadier. After 200 years, when he finally worked out the trick with the Teselecta and got around his own death, he'd never be able to see them again (without crossing his own timeline), and they wouldn't be there when he needs them in series 7 and the anniversary season.