Tag Teams increased because there were unfounded rumors that alt arts (or the equivalent of alt arts) would be disappearing in Scarlet/Violet. And as @tm26 mentioned, fewer proportionally were graded at the time that people started to buy them up, and the rest is history (supply/demand).
You are right that Pokemon wasn’t as big in DPP and BW, but there were a lot of children who played the games. And there should be some level of cross-pollination between cards and games. 