Spring-flowering bulbs have a growth cycle that sets them apart from most other plants. They make roots in the fall, bide their time through winter, emerge and bloom in spring, and go completely dormant in early summer.
During their brief period above ground, spring-flowering bulbs must store up enough energy to survive their long dormancy (bulbs are very much alive in their dormant state), produce roots, and send up leaves and flowers again the following spring--in that order. That is why it is important to let the leaves die back naturally after bloom. If you cut the leaves early, you force the bulb to make sacrifices--starting with the next spring's flowers.