We don't even get all the English-language culture there is around the world. Easy example: most of us are totally unfamiliar with popular Christian media.
Really, the appeal being made by people objecting to this site is that Black people shouldn't have sites that nurture that kind of content, because it somehow squicks white people out. That is a weird argument to make, and not one these founders should take seriously.
At least some people are arguing that it should exist, but should not be marketed to the demographic it is designed to appeal to, because it squicks white people out not that black content exists, but that people marketing it acknowledge that it is designed to appeal to the unmet needs of black consumers, because white people want to buy it but not if the marketing says it was designed to meet black interests.
Well, sure, because that's not their target market, but also because there isn't really a single predominant 'White culture' in the U.S., distinct from mainstream culture in general, in the same way that 'Black culture' was united by centuries of slavery and cultural destruction.
But you can certainly find media out there specifically targeted at people of Irish descent, Spanish descent, British descent, etc. It's just less of a mass-market thing because those groups don't have as much in the way of a distinct culture from the 'mainstream'.