Curriculum learning. It is pedagogically useful to teach simpler and easier versions of something before teaching the harder versions.
While you likely always have a calculator with you which can do division much more quickly than you can do long division, if you want to teach students more advanced math, it is nonetheless useful to have previously taught them long division of numbers, so that you can teach them long division of polynomials.
If students haven't learned how to do long division of decimals, and how that works, it is harder to teach them to do long division of polynomials.
Of course, nowadays there are computer programs which can do long division of polynomials more quickly than a person can, but this is just an example.
Suppose there are a sequence of levels, where for each level n, it is much easier to teach someone level n+1 if they already have an understanding of level n. If computers can do levels up to level k faster than humans can, it may still be useful to start teaching someone at level 1 and then proceed to level 2, and so on, even though computers can already do those levels, until finally it is time to teach them level k+1 which we have not yet managed to teach computers to do.