Because people are stupid! I had customers at MAC who would bypass the eyeliner testers and pull the live eyeliners off the wall, which were on the wall directly behind the testers mind you, and open them and swatch them in their hands. It happened to the foundations all the time too. It's like the big ass tables full of product tester were completely invisible! I made it a point to tell them that now those products needed damaged out because they had opened live merchandise and used the product. Their excuse was they 1. Didn't know there were testers. 2. Did see the testers. or 3. Couldn't find the testers. I guess no one ever taught them to ask for help
This is why i think live cosmetic products should be behind glass.