The words why, wye, y sound the same but have different meanings and spellings. Why do why, wye, y sound the same even though they are completely different words?
The answer is simple: why, wye, y are homophones of the English language.
For what purpose, reason, or cause; with what intention, justification, or motive: Why is the door shut? Why do birds sing?
The reason, cause, or purpose for which: I know why you left.
Usage Problem On account of which; for which: "The reason why [regular verbs] are called regular is that we can predict what all the other three forms are” ( Randolph Quirk).
The cause or intention underlying a given action or situation: studying the whys of antisocial behavior.
The letter y.
An object shaped like a Y.
The 25th letter of the modern English alphabet.
Any of the speech sounds represented by the letter y.
The 25th in a series.
Something shaped like the letter Y.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.
If they are spelled the same then they are also homographs (and homonyms); if they are spelled differently then they are also heterographs (literally "different writing").