Posted: 14/04/2014 at 07:05
Evolution and numbers, Mike. A typical plant will produce about a billion pollen grains. Many plants, while being capable of being pollinated by many different insects, have evolved to use one or two pollinating species in particular which they attract in a wide number of ways (eg by mimicking insect mating hormones); This makes it more likely that a "preferred" pollinator is more likely to visit another plant of the same species and thus transfer the pollen.
The downside is that these interactions are so complex that the humble human race is unlikely to ever be able to collate all of the information, so we will continue to only find out when our activity leads to the extinction of yet another species. A good example of this complexity is the Brazil nut, which was studied for decades (possibly over a hundred years) before it was understood: