If you take a look at the box, there’s no warning that tells you not to sit on it. However, seeing as how it contains a mirror, most people would assume that planting your bottom on the box in the first place would be a bad idea. This lady, however, didn’t have time to read or assume.
For all we know, she might’ve had a long, tiring day of mirror shopping at Target and needed to rest somewhere. She probably could’ve found another place to sit, but nobody has the time to walk the tens of feet to find it.