Oh, and Bachmann was undoubtedly taken aside by someone in Republican leadership who explained to her that her bills/committee assignments/financial problems/whatever would be looked at in a much more favorable light if she were to step aside.
At some point, the party looks after itself if someone's campaign goes too far off the rails, as it makes the rest of the party look bad and it's divisive. That's why Perry won't stick around all the way to the convention - after SC, someone will have the same conversation with him.
The only exceptions are people like Ron Paul, who has a long history of not caring what the party thinks of him, and just running the way he wants to run. He knows he can't win, but staying in the race and being in all the debates gives him name recognition, which helps him win races without any help from the national party. They, in turn, tolerate him in order to boost their numbers in Congress.
It's all complicated, but most of it revolves around the dollars. If you ever wonder why someone is doing something in Washington that seems strategically stupid on its face, it's probably down to money.