Because she was right and (presumably) helped stop an attack on America? When Estes and co. failed? I mean, that's reason enough to reinstate her. I would've been fine with four, five seasons with Brody but it's clear that, at this speed, they're running out of plot, and fast. Only worry with a Carrie only lead (and presumably another threat to investigate of a much different nature, so not another love interest please) is that she could easily turn into a Jack Bauer where no one believes her despite the fact that she's always right. That's lazy and stupid. But I have faith that the writers can come up with a convincing direction to take this series, with or without Brody.