In addition to all the other reasons given (large constant, etc.), these faster algorithms are also often less stable numerically, as another poster alluded to

In addition to all the other reasons given (large constant, etc.), these faster algorithms are also often less stable numerically, as another poster alluded to above. See, e.g., https://en.wikipedia.org/wiki/Strassen_algorithm https://en.wikipedia.org/wiki/Strassen_algorithm .