They aren’t farming, they’re foraging, and have evolved symbiotic relationships through evolution. The plants get a benefit by getting pollinated, the bees get a benefit by having more flowers to feed on.
Since they need pollen, bees who developed those little hairs are/were able to out-compete bees who didn’t have them. They’re able to carry a lot more pollen and incidentally transfer it, spreading it around, so the new bees are better pollinators. That helps plants produce a lot more flowers, so it’s truly a symbiotic relationship- one would not exist without the other. Since wasps are omnivores, the evolutionary pressure to specialize isn’t as strong.
IIrc, there are some wasps who have specialized relationships with certain plants and flowers too, driven by evolution- the flowers depend on the wasps, and the wasps depend on the flowers.