Lets turn the question around: Why do you think 0 / 0 = 1? You can't just say "A number divided by itself equals one, therefore the result for this calculation must be one", that's backwards. Mathematics is based on logic. A rule is made based on the facts, not the other way round. Give a mathematical proof that 0 / 0 = 1 and then you can state that any number divided by itself equals one. Until then there is no such rule or at the very least zero is an exception to that rule.
Frankly though this is all beyond the scope of this forum. This isn't the place to try and redefine fundamental tenets of mathematics, it's just a forum for an IRC client and its scripting language. Division by zero being undefined is a well established fact in maths, I'm certain there are many many places on the internet where it is explained much more clearly and in far greater detail than any answer you will get on this forum.