The question is “why?”. The political manuevering part is basic, but that assumes he is covering up.
Consider this example. Say we criticize the president for his handling of the economy, jobs, debt and other legitimate topics. With the birther issue unresolved, he can just paint us as a bunch of fringe, wacko kooks and use it to discredit our positions on those issues.
With the birth certificate revealed, if we STILL continue down this path, we look even worse than fringe, wacko kooks... we look like a bunch of idiots who are in denial and completely out of touch with reality, and that sinks us even more.
That's why we need to stop pushing this birther nonsense. It is done.