She still has a career because she's a bankable star. Here are the worldwide grosses for her last 10 major studio movies (yeah, I've got time on my hands):
Horrible Bosses: $206
Just Go With It: $214
The Switch: $49
The Bounty Hunter: $136
Love Happens: $36
He's Just Not That Into YOu: $179
Marley & Me: $243
The Break-Up: $205
Rumor Has It: $89
6 films with healthy profits, and 4 that either broke even or made a modest profit due to their low budgets.
Aniston movies don't cost much, so they're lower-risk. And they have a nice upside.