It’s about respect for the reader or listener. Using correct language eases the burden of deciphering what you are trying to say by using consistent forms. Otherwise it take extra effort for them to unscramble your words and figure out your meaning.

And yes, of course someone can figure out that when you say “me and Mike” you almost certainly mean to say “Mike and I”. But you’re making it harder for them by not bothering to learn or use the correct form.