https://en.m.wikipedia.org/wiki/List_of_apple_cultivars
There used to be more than the current 7500 cultivars. Many went extinct. There are groups that scour abandoned homesteads looking for surviving trees of lost varieties.
One reason there are so many is that apple trees are readily planted, but each new tree produces a completely different variety of fruit. Rule of thumb is that 1% of trees produce something edible, 0.1% something good, and 0.01% something commercializable.
For this reason, almost all apples you eat come from clones. (As they have been for 100's-1000's of years.)
Now we have more choices, which is good because apples are a species that produce offspring that is frequently quite different than the parents. Meaning every single one of those supermarket apples is the product of a long dead tree being propagated.