Why are pizzas and “pies” have their own day?
It’s Pi(e) day.
Pi (the Greek letter π) the constant roughly about 3.14, is used in certain mathematical contexts (geometry, trigonometry, calculus, etc.)
But stores interpret that in a new day and age added to the have popularized it (especially pizzerias and bakeries) as a price tag of 3.14, which resonates with the laymen better.
Greek is probably one of the most well-known alphabets outside the Latin. It is also the parent of the Cyrillic alphabet, found in languages like Russian and many others. The Greek is also used as the New Testament Scripture, and the Septuagint translation of Old Testament.