You are also applying mammalian standards to a plant. Trees may indeed be capable of living a very long while, but that does not mean that such lives are normal. A tree can live a full and productive life, reproducing and spreading many times, centuries before its total lifespan. There is also some speculation that trees may be immortal, that if their growth is artificially managed that they may just never have to die. Plants are different than mammals. They don't all have the same definitive life cycles.

For many cities, the goal is a healthy and sustainable urban canopy. Arboriculture has advanced a lot in the last hundred years, and we've made a lot of mistakes.

Eg, inappropriate species like Big Leaf Maple in inappropriate locations, like under power lines. Bad pruning practices. Planting monocultures (Elm). Boxing in roots.

As sick trees come down, better practices can lead to better trees for the next generation.

For some common species, 100 years is downright old, and reaching the end of their natural life anyways.