Because its very easy to scam By Juicy Pictures. But if You are a good user of Pinterest you should know how to be safe from these scamming spamming.
Its not a very hard work or its not necessary to learn a lot of things to be safe in pinterest. Just use a simple tricks. I am sure most of the internet user knew about the Google image search. You can find out any images original source by image search in google.
Whenever You see a lovely offer in pinterest(And if you become interested on it) with a loving picture just put your mouse on the image. Copy the link and Do a google search in Google image search. You will found some result about that image and hopefully you will get some valuable information about that image.
Its a very easy trick. But It can save you from some Unwanted problems.