Trees survive transplanting not because you save roots, but because the tree can easily grow new roots. One inch diameter roots are the ideal size for generating new roots. High vitality trees have high starch levels to survive transplanting. Maintenance budgets are usually insufficient. The budget consists of planting and removals.
Some funds are available for pruning and other tree care.
They use more food than they can manufacture. The food hierarchy for carbon allocation is for maintenance first, followed by new roots, leaves, storage, and trunk diameter. Tree defense against pests is the lowest priority. We focus too much on tree growth. Thus, because of the hierarchy, when we focus on growth, the tree's defense against pests is diminished.