Why do we say 'good, better, best' rather than 'good, gooder, goodest'?

According to an etymological source - there is a widespread pattern of irregular comparatives and superlatives for the word 'good' - across several languages. Latin - bonus, melior, optimus. It holds true in German - gut, besser, am besten. If you look up the etymology of 'melior' and 'optimus' it might explain further.