in divison why should the remainder not be greater the the divisor
If the remainder is greater than the divisor, then this means that another divisor could have been added.
For example, 7/3
If I said the result was 1 and the remainder was 4, 3 can fit into 4, meaning that the remainder (What remains when you have calculated the result) would be incorrect.
The correct answer would be 2 remainder 1.
The remainder is there to simplify division. If I did 7/3 normally, it would be 2.3333333333 recurring, giving us an "ugly" result. The remainder therefore gives us whole number results.
You shouldn't have a remainder greater than the divisor, because it means that another number can be multiplied.