A yard full of nectar flowers can feed adult butterflies without providing anywhere for the next generation to grow.
Host plants feed caterpillars
Butterfly and moth larvae often have specific plant relationships. Native milkweeds are the best-known example for monarchs, but many other butterflies use different native hosts.
Expect some chewing
A functioning host plant may have eaten leaves. In a habitat garden, limited cosmetic feeding is often part of the goal.