Why would a grouped image break when you resize?

How come I made so many edits to this cube, I had to place all shapes to hide the lines, I had to carefully place the grey part on the cube, so I grouped it, made it bigger and the whole thing messed up. Im so p#ssed. What is the point in grouping if this happens. I press undo and the whole thing is still a mess, it just made it even worse.