Those 4000 native species tend to pollinate within a specific niche, which is wonderful, unless you are, say, an almond or orange or apple farmer.
The advantages of introduced/naturalized honeybees (bees of genus Apis, primarily Apis mellifera) are:
1. They co-evolved with the Old World crops that make up most of our ag.
2. They are in any case promiscuous pollinators, so they will even pollinate ag species they have never seen before.
The disadvantage, of course, can be displacement of native bee species that preferentially pollinate native plants with cascading effects on native plant populations. Between European bees and European earthworms, the environment in North America has been radically changed since they were introduced in about the seventeenth century (sixteenth in South America).
