Just to be clear, Terms of Service (ToS) and End-User License Agreement (EULA) are not the same thing, and cannot be used interchangeably. Try to be clear about which one you're referring to.
Ultimately, forums like GBATemp have zero reason to care about breaching EULAs. What they do have to care about, however, is the laws of the country in which their servers are hosted, because it is those laws that will apply to them.
If they're hosted in a country with copyright legislation, they are subject to those laws. In which case, distributing copyrighted material without license to do so would constitute a violation, which an interested party such as Nintendo could bring to the attention of authorities in the case that they wanted to get serious about pursuing legal action. It would then be in GBATemp's best interests to disallow such content to prevent that.