How come it seems like half of the doujins in my searches end

Large amount of girls, something for everybody's tastes.

>>15651768
Being a pair of long running video game series with loadsa memes rather than a flavour-of-the-season anime.

Established and devoted fanbases. Over a hundred girls between the two. It's not rocket science,

>>15652249
There's probably 100 girls in each other them separately.

Touhou should get some weird anime like Xenoglossia.

>>15652254
There's close to a hundred Touhou girls but I don't keep up with idolm@ster so I wouldn't know.

>>15651768
They are both franchises made to satisfy otaku's lust.
They did a good job.