It seems a perennial misconception that a tree is a tree, one is much the same as another and all are easily replaceable. This is fundamentally not the case. Trees are such long-lived creatures and go through so many phases in their lives that the loss of a mature specimen to be equitably replaced by saplings is simply a nonsense.
Trees are living organisms in their own right but much more, they are habitats for so many more. Whether this be nesting sites for great tits, roosting holes for bats, shelters for squirrels, nut-sources for dormice, food for sycamore moths, focus for purple emperors, nourishment for fungi or substrate for mosses and lichens to name but a few. Some of these myriad functions are provided by younger trees, but the scale, quality and extent all increase with the age of the tree and some rarely develop until the tree reaches maturity or beyond.
I came across this low-hanging branch on an oak tree and was distracted a while by the sheer abundance of mosses and lichens with which it was carpeted. I think it nicely demonstrates just how valuable these older trees can be in their provision of a platform for other species.