The reason is that in inverse variation the product of the two quantities ai always a constant - that is, if x varies inversely as y then xy = k ( a constant not equal to zero)

If x = 0, then the product of x and y would be 0 for every possible value of y so it would not be inverse variation

For instance if y=2 and x=0

When we double y to 4 x should be halved - but it remains 0