It’s always been a “pet theory” of mine that this reversal was due to Reddit becoming mainstream, and that it’s initial nerdy/techie user base preferred cats to dogs.
I have a competing theory. Dogs started to become wildly popular during the early to mid 2010s, when millennials were graduating from college and getting their own apartments/homes. It’s well known that millennials are having far fewer children. I believe that millennials started getting dogs instead of having kids, and this caused a huge spike in the popularity of dogs. This is also consistent with everyone suddenly starting to refer to their pets as their “children” or “fur babies”, because they are literally replacements for human children. Anecdotally, as a millennial, I have seen almost everyone I knew in high school get a dog over the past decade.
Your intuition is correct here. OP is wrong. An infinite set of branches of the wavefunction does not necessarily imply that everything you can imagine must happen somewhere in that wavefunction.