look, the guy who invented zero said:
a*0=a
now, if we didn't know that you can't divide by zero, to find out what result does dividing by zero leads tom you'd say:
a/0=a
now, that's exactly the same as
a/0=a/1
and because of that you can say:
0=1
which is, of course, in most numerical systems and known universes, wrong, so therefore you say you simply can't do it.
There you have an easy explaination, now stop asking why.