I believe the idea that females cannot mate with multiple males has been disproven in bonobos, where females often have many male partners. The story that gets told is this confuses paternity, which creates a broader safety net for resources for the baby.

So it might not be quite so simple as initially thought. Be wary of much of the evolutionary bio's attempts to explain why things are -- often, the proposed theories are one of many ways to explain the evidence. Little thought is given to the other options.