Why Sanskrit has ekvachan, divachan, and bahuvachan??

IIn English, there are only two numbers: singular and plural. In Sanskrit there are three: singular, dual and plural [एकवचन, द्विवचन, बहुवचन]. The noun undergoes appropriate inflexions to indicate the number. Example: फलम्= fruit;  फले= two fruits; फलानि= many (more than two) fruits.

There is no specific reason for the division of number into 3 in sanskrit.