I've been seeing a lot of Wriggle x Yuuka pictures lately...
what's up?

Sorry for asking so many questions recently, but I don't want to make any assumptions and offend people as a result...
Just let me know and I'll shut up...

I'd say pure fandom, like the majority of the pairings in Touhou.
In fact, they don't even have a confirmed relationship of any sort in the games, so they probably never met in canon.

but why those two?

There's a running thing with green-haired characters being depicted together, e.g. post #189878 post #183938
Same with weak, plot-irrelevant characters like Cirno, Mystia, Daiyousei, etc., post #185192 post #165956 post #155826

So why is there more pics of Wriggle and Yuuka than Wriggle and Mima, Eiki or Daiyousei, etc?

I think the reason is the relation between insect x flower.
Plus they make a nice couple :3 (yeah, bad engrish... you know the rest)

Bansho said:

So why is there more pics of Wriggle and Yuuka than Wriggle and Mima, Eiki or Daiyousei, etc?

It's because Wriggle is a bug and Yuuka is a flower youkai. The two click based on their element's relationship with one another. Mima is popular but since she hasn't appeared in any new games, there isn't much to do with her while Eiki is really judgy, and Daiyousei is a mystery in terms of backstory and element.