One of the things that makes honey bees great pollinators is that each bee tends to specialize in a particular food source. In other words, they will visit the same kind of flower over and over again. It's more efficient to learn how to get nectar or pollen from a certain flower, and then just keep working that flower until it's no longer productive. Under close inspection, you'd see that each flower is its own little puzzle, and the bees minimize the time spent unlocking the puzzles if they don't bounce from species to species. This is also good for the plants, because it means they're visited by bees that have often just come from another flower of the same species--vitally important when you rely on animal pollination for survival.
Incidentally, it's a late year for foraging here in Missouri. Compared with bloom times from previous years, we're almost a month behind. I'm not complaining...it's comforting to have an unexpectedly long winter after so many unexpectedly early springs.