Credit Christopher C. Witt
Hummingbirds such as this Buff-tailed Sicklebill specialize in nectar feeding.
But other species of birds, less specialized to nectar, also visit flowers for a taste of the sweet stuff.
The flowers they visit likely have a more open shape, with nectar more accessible to a non-specialist’s bill. The sugar they sample is probably different from what hummingbirds prefer.
As flowering plants and birds co-evolved, each to benefit from the other, it seems likely that plants evolved the type of sugar best suited to the pollinators on hand. It's a win-win for all concerned.