Both of my homes are in old neighborhoods with lots of mature trees. Such places are artificially rich habitats for squirrels, leading to huge populations. Water is always available, landscapes provide large amounts of food, and people feed birds. It would not surprise me to know that over 50% of seed intended for birds is consumed by squirrels and rats.
Then there is the almost complete absence of predators. My current neighborhood has a permanent population of coyotes, bobcats, and foxes, but they can't keep up. And the squirrels use there own habituation to humans as protection from predators.
My neighborhood has an extensive greenbelt system with a permanent stream and acres of forest. Is it full of squirrels? No! In a semi-natural environment squirrels have to work for their food, struggle to find safe nests and tree cavities, and avoid predators. One almost never sees a squirrel in the greenbelt. A block away in the neighborhood there are a dozen for each lot.
The point of this rant is that the population of squirrels in such neighborhoods is NOT a natural phenomenon, but directly caused by human changes to the environment. I would be extremely happy if wild predators could eat the excess. But they cannot. Until they can, my dogs, traps, and pellet gun are the apex predators.