I'm not so sure

She fills a particular character niche and there not really any other character that does that, both in design and in her breed of insanity. And the internet went wild for 'mime/clown-ussy' the other year with that ace atorney clown and derpixion smut animation.

The joker himself surged in popularity too, both with the original nolan Batman, and with the joker film. Rising tide, Harley is going to get more popular too. And the batman cartoons and games the last decade or so have had some bangers. So I do think there's a nugget of truth to her popularity being organic, at least originally.

They saw that and attempted to subvert it, and its now an inorganic push, sure. But I do see how she originally was somewhat popular.