Are schools failing to teach it, or do some lessons fail to stick through the decades depending on how much math you’re doing? Schools have no control on what your older relatives have been up to.
Today’s Facebook grumpy posters would be the same kids doing “New Math” in the 1960s: https://en.wikipedia.org/wiki/New_Math - just something to consider
My older relatives are the ones I see repost these inane order-of-operation tests, getting the answer consistently wrong.