Quite simply, "reality" is the sum of all existents. Nothing can exist outside of reality. To rephrase this, approaching the point from the opposite angle, non-reality does not exist. Reality, as the sum of all existents, encompasses all that exists - it is not suspended within non-reality.
Let's start with an infinite, all-encompassing God. The mythos of most monotheistic religions posits that God is infinite - that He has no beginning and no end. So long as God is all that exists and He is infinite, there is no problem with this assertion. At this point, "God" is interchangeable with "reality" - the two terms are redundant. However, this is an issue of semantics and not ration, so we'll leave that aside.
Now, this infinite God, in the tradition of most monotheistic religions, one day sets himself to creating a universe. Here is where the problem arises - the moment He creates a universe - or anything for that matter - separate from Himself, he is no longer infinite. To put this in simpler terms, suddenly we have two entities: God and His universe. They must be suspended in something - as non-reality does not exist, these two entities could not, together, make up all of reality, suspended in non-reality. Whatever it is that they existed within, together, would be reality. Here the problem of infinite regress arises: who or what created the reality that God and His fresh new universe are presently existing within?
The only solution to this is that reality is infinite. Which is to say that reality is all that is, that, by definition, nothing can exist outside of reality and reality cannot be suspended in a non-existent non-reality.
Why is this truism not universally accepted? There are three reasons.
1.) Many people have simply not been introduced to this, Kant's famous formulation.
2.) Of those who have been introduced to this formulation, many are, for personal reasons, unwilling to accept it. I'll not outline these reasons, as I trust in the intelligence and world wisdom of those reading this to conjure up a good number of cases in point on their own.
3.) Of those who have been introduced to this formulation, many quite simply lack the imagination and intelligence to reach the level of understanding of the concept of the infinite required to grasp it. I realize that this sort of language makes certain types bristle, but it is the fact of the matter.
And that's really all there is to it.