It's odd that in English you have two different words for third person pronouns (he, she), yet the second person only gets one for both singular and plural (you). In Finnish for example we have it the other way around, we only have hän for both genders in third person but we distinguish singular (sinä) and plural (te). It's like there is a set amount of pronouns a language can get and English went for separating genders instead of individuals.
There actually used to be a pronoun for singular second person as well in English language. There were actually even two of those. But not to distinguish gender, just accusative and nominative forms. The same was true for the plurals as well.
There are many explanations why all these additional forms have disappeared, but nobody knows for sure. The fact is that the words thee, thou and ye (singular accusative you, singular nominative you and plural nominative) have mostly disappeared from the English language and can only be found in some old texts.
One of the theories suggest that those forms addressing people become offensive when the plural form was considered more formal way. As the plural form has become the common, the rare cases when they are used in modern context has actually become the more formal way.