There's a huge difference between mean-spirited user-generated shitposts and quirky advertising campaign. You're talking about the latter. Crucially, an advertising campaign is carefully crafted and gets approval, whereas millions of shitposts you might potentially advertise online are not and do not, and many of them pose a brand risk to be associated with.

So I ask again, show me examples of advertisers that enthusiastically advertise on shitposts.

Sure, and no true scotsman puts sugar on his porridge.

Your own chosen example was Elon Musk recent twitter history. Debating the difference between your chosen example and Dennys to identify an obvious principle that distinguishes them is asking people to play calvinball with you.