Well, it all comes down to copyright law.
The IOC’s website makes it clear: no part of their site or its content may be copied, republished, or reproduced without explicit written permission.
Let’s face it—who’s really going to bother asking for permission to share a meme?
The Digital Millennium Copyright Act (DMCA) also comes into play, and some unfortunate meme sharers have received stern emails warning of copyright violations.