If you look at a forest or other natural areas, most of the trees seem to be doing perfectly fine without people having to come in and provide any care. So why do the trees in our neighborhoods need so much attention?
Human-made, urban environments are very different from what trees are used to and can have some very stressful affects on them. These include: soil compaction, air and water pollution, limited soil and water availability, limited canopy space, more extreme temperature changes, and an increased chance of physical damage above and below ground.
In such a harsh environment, sometimes they need a little help in order to coexist with humans.