Same reason you don't introduce liquids or other mediums into products (shadows, blushes, etc) that they aren't meant to be introduced into. They start to grow mold and other nasty lil things. If it dries up, you either try and salvage just what you're gonna wear just for that day, or you suck it up and chuck it. You NEVER put liquids into a cosmetic, close the lid, and tuck it away. That's just asking for an infection to happen. Same thing applies to mascara. I keep seeing people posting the Beautylish add that promotes adding visine to your mascara when it starts to dry up and i wanna throw up every time

Please people. DO NOT DO THIS!!!