Eevee is more popular within the "hardcore" Pokemon fandom (but not by a landslide). This is due to the wild popularity of the eeveelutions, its cuteness and also Pikachu's overexposure, which is why some don't like it.
However, Pikachu is more known and is essentially the face of Pokemon so newcomers and Go fans are inclined towards it.
And it's clear that Newcomers & Go fans > Hardcore Pokemon fans, causing the results @Icy Wind mentioned.