Let me attempt to give you an answer. If the threads are not cross threaded, the the bolt is going in parallel to the hole. Imagine pushing a peg into a hole. If the peg is perfectly aligned with the hole, it goes in pretty easily. Now imagine trying to push the peg into the hole at a slight angle. Pretty soon the nose of the peg is trying to push its way into the side of the hole. The deeper the hole and correspondingly longer peg, the deeper the peg has to go into the side of the hole if it is to maintain that angle.
If the hole is shallow, once the peg pushes through the other side, it has finished distorting the hole so it gets a little easier, not as easy as if it were straight, but a little easier. There is additional friction from the pressure on the side of the hole due to the angle.
So if you had a hole that was not very deep, four threads for example, and you cross threaded the bolt, it would get harder to turn with each turn until you finished the fourth turn. Now you are through cutting new threads, but the bolt will still be harder to turn than a properly threaded bolt. A deep hole just keeps getting harder and harder until you just cant turn the bolt anymore or the bolt breaks off and now you have a bigger problem.
A cross threads bolt is not only trying to cut new threads, it is also going into the hole at an angle just like the peg above, so there are two forces working against you.