Pollinators mature at different times

Pollinators mature on varying schedules. Generalist pollinators have to adapt their preferences depending on who's flowering when. So from one flowering season to the next, the participants and patterns of matchmaking can drastically change. With all those variables, you can understand the importance of generalist pollinators, like bees, to the stability of not only a crop harvest, but the entire network of plants and pollinators we see in nature, and rely on for life.
Next time you see a bee fly by, remember that it belongs to a complex network of matchmakers critical to the love lives of plants all around you.