Why is it that when a person tells you there's over a billion stars in the universe you believe them, but if someone tells you there's wet paint somewhere, you have to touch it?
Basically, that's actually a decent question. Part of the problem is our own 3 dimensional locked sences and thought patterns tends to keep most from wanting to accept the idea of an outside hyperspace of multiple dimensions. If one says there is a billion stars in the sky most may not even try to count them. But they can look up and see in some regions a decent amount of stars and at least make the assumption the number sounds close to reality. When you start to mention other dimensions we simply do not have the ability to look out and say, well I see this and that sounds about right.
If anything its interesting that some people who have problems with there being a hyperspace will also speak of God or Creator who by definition would exist outside of all we can see. Now where is the logic in that one?