Perhaps, some of our desires are incompatible, either with what is best or with what can be. Since herbivory causes a loss of available energy, plants have developed different strategies to control or limit it. Some herbivores have adapted, thriving on the chemicals or neutralizing them, perhaps even using them to aid their own survival. In the distant past, whatever strategy was adopted may have discouraged activity from herbivores far more voracious than the ones we find now.
Some plants respond to herbivory by modifying their architecture.
Bushier plants can result when lateral bud development is stimulated by the destruction of growing tips. Root-feeding insects may stimulate similar changes in root systems. Some plant species have developed mutually beneficial relationships with ants. Most ant species do not feed on plants, but by wandering all over the plant they discourage the presence of other insects, some of which are herbivores at some stage in their lives. Bull-horn acacias provide homes for ants in their thorns.