Bees have become at risk. Environmental problems, including an over-abundant rainfall, the indiscriminate use of pesticides and deforestation destroying bee habitat, has resulted in poor production of tree fruits and other vegetables and fruits which require pollination. As if this wasn't bad enough, along came a tiny creature called the varroa mite, which began to parasitize and infect the bees in their larval state, causing stunting and death. Many folks are now trying to attract the mason bee, a tiny bee immune to the varroa mite, which likes to live in a tube-shaped house, and is an important orchard pollinator. It makes sense that the workhorses in your beneficial-attracting garden will be the tried and true varieties.
Many new varieties produce little or no nectar, and even no pollen at all.
In addition, for novelty's sake, a plant breeder will create a hybrid in which the structure of a flower is altered. Double flowers seem less beloved by bees than single, perhaps because it is harder to get at the nectar amongst all those petals. Plant buddleia, honeysuckle, sweet-smelling roses, four o'clocks, single stocks, single carnations. Virtually all sweet-smelling flowers contain nectar which pollinating insects need. Remember that bumblebees are far more attracted to old varieties of larkspur, nasturtiums, snapdragons, foxgloves, petunias, single hollyhocks.