After the male hummingbird has impregnated the female hummingbird his job is officially done. The male must stay out of sight and therefore has nothing more to do with the female or their young. Why is this? The answer is due to the fact that the bright, flashy colors on the male are a danger to both the female and the young because this could attract predators which would put all at risk.
It is for this reason that the female is responsible for building the nest, feeding and raising the young on her own. The female wants to try and ensure the best possible chance at survival for all.