Because most climate activists are seen as spoiled kids who don't have jobs or other obligations. So when they protest it's seen as them inconveniencing regular people, whose daily struggles they can't even fathom, all because the protestors have nothing better to do.

Meanwhile farmers are seen as hardworking with strong community ties. So when they take time and equipment to protest something, it's seen as something that must be important and worthwhile. Plus, there's a deep feeling of unease that comes over most people when they see things that threaten to fuck with the food supply.