Why are women obsessed with becoming skinny?

Advertising, the media etc portray the idea that a woman has to be skinny in order to look good, when in reality we know that that isn't the case. Being slim is one thing but being skinny and skeletal is something else. The average size of a woman is the UK is a size 14 and the sooner the media starts portraying this instead of size 0-6's the better we will be and maybe then we wouldn't get so many girls at the age of 10 starving themselves