The bumblebees that you see early in the year are the queens that overwintered. They have no workers yet, and they need both nectar (for themselves) and pollen for the brood they are bringing up. The queens never touch my tomatoes in early season here, even when other flowers are scarce. They'll do a flyby speeding along in search of something good, never stopping for any of what we've got... That is because tomato flowers have lots of pollen but no nectar. Once the first brood have hatched these little bees will work the tomatoes really thoroughly, to bring home the abundant pollen for the next brood.
OTOH put out pepper plants or brassicas that bolted, and the queens will be humming 'thank you thank you!" and gobbling it up.