Division by zero is an operation for which you cannot find an answer, so it is disallowed. You can understand why if you think about how division and multiplication are related.
12 divided by 6 is 2 because
6 times 2 is 12
12 divided by 0 is x would mean that
0 times x = 12
But no value would work for x because 0 times any number is 0. So division by zero doesn’t work.