Clutter. In most of out toy/hobby rooms clutter is ever-present and no amount of tidying will ever banish it. In my own toy room every horizontal surface is fair game for clutter and even hiding a lot of it away in boxes and drawers fails to prevent it's spread.
The photos show but a small part of the issue. Above, on an area of shelf less than 2 feet square can be seen toys in at least nine different scales and several stages of completion/neglect. Below, well, all sorts of cr*p really.