Say I sell pink and white bicycles. You can order a bike with or without tassels.
I have 50 pink and 50 white bicycles.
Magento is going to create 50 pink with tassels, 50 pink without tassels, 50 white with tassels, 50 white without tassels.
That's 100 pink and 100 white bicycles. I only have 50 of each in inventory.
See the problem? Am I missing something somewhere?