To answer the question given in the title: Every country has their own laws. Some of the limitations are based on international agreements, so approximately the same law can be valid in many countries. Some countries may not have such regulations.

There are many people who do not respect laws at all, but some people do not respect copyright because it's today very easy to steal pictures, software, music etc. which can be distributed in the web.  They steal because they think they live in a place where the copyright owner has very little power to act. But often they for ex. do not print money because even the poorest and most overpopulated country will act fast and violently when that happens. 

The ability to want to steal is between one's ears. The thief of intellectual property may explain to himself for ex. "Actually I didn't steal. It was available with no obstacles and all in all I did not take even a single atom of anyone's property." 

In USA the asked law is the Copyright Act 1976: https://www.copyright.gov/history/pl94-553.pdf

I'm afraid ordinary people do not want to study the linked text. Fortunately there are lawyers who earn their bread by being able to read, understand and apply texts like this. Different organizations publish practical copyright guidance for their members and users of the creations of the members. You find easily easy to read explanations also by searching for Copyright Act 1976.

Finally the websites which distribute legally creations as files and the distributed files themselves contain the license - the exact conditions and limitations of the usage.

Note that there are other forms of intellectual property ownerships than copyright. If a person creates something without being hired by any employer he has automatically the copyright. Business companies often register trademarks to prevent others to utilize their name or the look and feel of their products.