I recently observed that a non native speaker of english use the word "destroied" instead of "destroyed". It made me wonder why it is not "destroied". For "cry" it is "cried" but not "cryed". How it is determined or what rules decide what to use?
You cited cried. Do you know any example where -oy becomes -oied instead of -oyed? I don't. How about -ay or -ey or -uy (if any)?
For -oied the Oxford English Dictionary (subscription required) has only two: ototoied, past tense of the verb ototoi; and voied, alternate spelling of void.