From my understanding:
I get that for honeybees, they need the nectar to make honey (their energy food source) and the pollen is an additional, essential food source for them which contains protein. They collect both nectar and pollen from flowers.
For other pollinators like wasps, they don't make honey but they still need to eat nectar and pollen which they collect from flowers.
Though these pollinators benefit (survive/thrive) by collecting nectar and pollen from flowers, they also help plants to reproduce by carrying pollen between them and depositing it.
But why do they transfer pollen to other flowering plants? Of course this allows certain plants to reproduce, but that doesn't explain why these pollinators care about helping plants reproduce. Are they little plant farmers who actually realise that transferring pollen and therefore making more plants, would benefit them? That would seem to demonstrate pretty high-level intelligence and foresight, planning wouldn't it? Or is it just incidental that they're going between flowers collecting nectar and pollen and happen to drop some pollen from previous flowers along the way?
I really struggled to find any information on the "WHY" of what bees are doing, from their own psychology point of view.
Bees are messy. When they go to the flower, it gets all over them.
The flowers are designed such that the pollen does this…. Because the flowers that do spread better. The bees are just there to get food, but while they’re going about getting food, they’re making an awful mess, and the flowers benefit.
I've been carefully deadheading that bull thistle that grew in my yard this year because I don't want only bull thistle in my yard next year, but the bumble bees just freak out over it, so I don't have the heart to get rid of it while it's in bloom. It's about six feet high and very thorny.