With certain exceptions, nothing a brand lets you see is by mistake. Every detail of a company's image has been meticulously crafted and fussed over. There's a reason, for instance, that McDonald's and many other fast food chains use red and yellow in their signage. (Those colors are proven to be the most eye-catching.) All this specificity, and the familiarity it builds over time, is what gives an air of unreality to seeing one brand cloaked inside another brand's logo.
In a post for full-service design hub Round Peg, Jenna Giles experimented with various brands by giving them the Freaky Friday treatment. Swapping the font choices and colors of Lego with Ray Ban illustrates some of the decisions that go into creating a logo. Making a brand seem playful or tasteful requires a lot of distinct choices, and it's clear how well those choices pay off when you see these kinds of clashes. Now just imagine how scandalized the average Hermès customer would feel to be associated with Dunkin Donuts.
Have a look through a few more examples in the slides above.
H/t to DesignTAXI