
Shota is...the opposite of loli? It basically means little boy, so in the context of BL, it's a story where a little boy is involved.
You can think Nii chan, Super Lovers, Boku no Pico, Shota Oni, and the like.
I don't know why they declared war, but my best guess is that in their efforts to sanitize the website, the underage stuff had to go.
Mind you, you can still find some stuff in here, but the tag "shota" was purged.

Basically, a lot of East Asian countries which a lot of these mangas are made of. Are cracking down on CP being drawn. ESPECIALLY with cases like Boku no pico which the whole point of it was to sexualize minors. I don't know where mangago is stationed. But I'm pretty sure that is why shota and loli is being turned down.
~ Urah
Has nii-chan from harada been deleted?