I have argued in the past that this is a manifestation of something that's been brewing for a while. What I mean by this is that the vaporeon copypasta became a sort of anchor point for eeveelution attraction.
First the eeveelutions are very sexualization, among all the Pokémon they have top tier rule 34 growth especially Glaceon, Umbreon and Sylveon aside from Vaporeon. The websites that emerged from Markiplier video also say the same story, people who partake in this inanity do find the eeveelutions attractive, and apperantly Ninetales as well. When it comes to the popular imagination having high amounts of rule34 is mandatory, high attraction works well too. This is why Pokémon like Gardevoir, Lopunny, Lucario, the eeveelutions form the back bone of Pokémon attraction, appear in videos and have videos and pictures made with some junior members like the fennekin line and Zoroark among others. This is also why Meowscarada has been rapidly climbing, in another thread I showed how frequently it's starting to appear in YouTube videos. Lack of sexualizition also mostly excludes Pokémon from this core, even if people find them attractive, such as Hatterene, Meloetta, Tsareena, Milotic and to some extend Primarina. Pokémon with good "attractive" rating but low sexualizition so they don't generally enter the public consciousness. Vaporeon already showcased both, not to the extend of Sylveon nor Umbreon, but they are there. The anime also recognized the place of the eeveelutions in this hierarchy via Meowth dream back in 2017.
So the blow up of the copypasta isn't that surprising, the materials were already there. While there is some shock value I would argue that it's driven by genuine eeveelution attraction in this context. As Smash or Pass has shown Pokémon attraction clusters pretty closely, even Gardevoir is only slightly ahead of all the top tiers.
