They skip leap years every now and then. And then skip the skip. Etc. The rotation of the earth around the sun and the spin of the earth on its axis simply don’t line up into a nice number.
Oh okay. Yeah I only have that rule of “every 4 years” in my head. I did some other programming exercise way back where we had some other rule, but I was thinking that it would end up being the same.
The boring answer is that in physics a year is just defined as the time it takes for the Earth to orbit the sun, they don’t care about calendars and leap years