From my point of view, tubes are essential for transportation etc.. but if I had an uncut sheet, $100.00 doesn't seem THAT bad to keep it mint forever and able to display.
And if you had, for example, 4 uncut sheets? Are you willing to shell out $400?
What if you had 10 sheets? 20?
My point is that at some point, it becomes impractical to store them in any way other than tubes, and so that is standard practice.