Copyright has been an issue for a long while and it's been much more contentious with the rise of the internet. Some jurisdictions have draconian copyright laws and some have effectively no enforcement for what whatever laws they might have.

Copyright enforcement is largely judged by a court system with jurisdiction for the alleged infringement. Defending against any accusation of infringement is expensive and more than one web site has shut down entirely after a cease and desist notice from a lawyer. Any web site with a revenue stream makes a target for lawyers eager to bill their hourly rate. Even just fanart ones with some ads. It's unlikely that most fanart will attract legal attention, but it might. Better to be safe than sorry.