In forests, relative density, relative cover, and relative frequency are weighted to determine dominance. In herbaceous communities, dominance is determined by relative cover and frequency. You need look only as far as your garden for the answer to this question. The typical North American garden consists of bluegrass or some other turf, a dozen annuals and perennials, and a few shrubs and shade trees. If you are a bird looking for food, visiting the typical garden is like going to a restaurant where there is only one dish on the menu.
Nature offers a smorgasbord to animals.
The diversity of ecosystems and species within them offers a complete menu for a rich variety of creatures. Our gardens can do a lot better. Plant thirty or even fifty perennials instead of a dozen. Use many different fruiting shrubs and trees. Choose half a dozen shade trees.