The reason why Japanese can have so many different pronouns is because of its grammar
Nominative case, accusative case etc. are marked by particles like が or を and plural is marked by たち, because japanese is an agglutinative language. That means you can easily substitute the first person pronoun for any other word and it would still fit in the grammatical framework. In English you can't do that, the pronouns are inflected fusionally, that means, you can't just substitute “I” for any other word, because the word would need inflected forms like oblique “me” or possessive “my” and there is just no simple way of constructing such words to mark these cases like in Japanese. This is also why in so many fusional languages the polite form is simply inherited from a plural form, because you already would have all the inflected forms for these words and needn't come up with new ones.