Zero is just as arbitrary as 32 but ever so slightly easier to remember. Anyone for whom that slight difference in remembering is actually a real impediment likely has other issues that require them to be under the care of others so it ceases to be relevant to them. At the other end, 100 vs 212 is of no practical use for anyone. Outside of the laboratory and manufacturing, people just boil water without thinking about the number associated with it. And in those settings, many other variables are tracked so the difference is of near zero consequence.