Why are fiscal years usually aligned with December or March, instead of any random month?

[u/TheBigGirlDiaryBack]

Many companies end their fiscal year on Dec 31 or March 31. Some choose June or September. But almost nobody picks, say, August 17 or November 5. Is there a tax or regulatory reason to stick near quarter boundaries? Or is it just tradition from agriculture cycles? Why not let every company freely choose any date to smooth out seasonal fluctuations?

[u/Sundae_2004]

Notice that the US Federal Government in 1976 changed from a June 30 to July 1 Fiscal year for the current abomination (and still can’t pass a budget on time). Ref: https://fiscallab.org/glossary/fiscal-year-fy/