The thing is, pollinators have to eat all year. You get more bang for your buck by planting things with long or repeated flowering intervals, or things that bloom at odd times. I've seen rosemary flower 3 times in one year due to sustained rainy periods.

And then there are predator species that need certain flowers for forage or shelter during some part of their lifecycle, like lady beetles or some predatory wasps with yarrow (a common volunteer plant in NA)