Not all Internet users generate the same amount of content. In addition to Americans being proud blabbermouths in general, people from wealthy countries generate more content than those from poorer countries. The US is among the wealthiest countries in the world.

Although it is not the most representative, nearly half of all Reddit users are American. American media outlets have immense global reach. You can probably name four or five American media outlets just off the top of your head, even if you’re not American. The USA’s geopolitical power means people are always talking about American politics or what America’s leaders are doing, which draws engagement from Americans like a lamp draws moths. 7 out of the top 10 English-language YouTube channels are American (fully or partially).

It’s pretty much impossible to prove, but I think the claim that Americans generate most of the content on the Internet is likely true or very close to true.