A moderator should be able to give some insight to the reasons being but I personally believe that your question is off topic never mind not very constructive it's important to note while the most of us are experienced webmasters it doesn't mean we are necessary in the position to answer copyright, trademark and other infringing laws. You should be seeking the appropriate legal advice from professionals in this field (I.E Copyright Consultancy's and Lawyers).
In your question about how do other sites handle legal matters, it is one or more of 5 possibilities:
- They ignore copyright law.
- They seek professional legal advice.
- They obey copyright laws and seek appropriate permission before publishing.
- They purchase the rights to use the copyrighted material.
- They use some kind of open license that allows the material to be published on selected platforms under the licensing terms of the agreement (i.e creative commons).
Quite frankly its very inappropriate to seek legal advice from people who could give you the wrong advice and then you will be found liable.