y do u pronounce to and go differently; i.e. "o" sound?

Answer 1

Because that's how it's spelt. Early English literatists chose to remember which form of vowel to use, instead of using accents like almost every other language that uses latin letters. for instance stay could have been written sté, mover could have been müvèr. It makes for harder spelling, but at least we don't have a keyboard cluttered with accents.