No it's random and arbitrary. Those couple degrees improve shelf life and allow for better extermination of many organisms, and higher temperature gradient allows the water to freeze faster, which is reflected in the quality of the product after thawing as it is less affected by wrongly formed and expanded ice. There is no "golden temperature", and so everyone flips it how they like it, and instead of what's actually right this is often dictated by convenience.

There are strong benefits to keeping your freezer at -80°C (-112°F), even, but at this point it crosses the line of practicality by both freezer cost and electricity consumption.

Also, the whole numbers argument is extemely weird. Like, do you know the difference between 71 and 72°F? Is it pronounced in any way? I can assure you, I cannot tell the difference between 21°C and 22°C. And where it actually matters (precise measurements etc.) you'll need decimals for both (and there's nothing wrong with them!)