why spammers / banned users show as active members ?

[Fossor]

Just moved 3rd forum from VB unfortunately with 11,500 spam accounts (thanks to broken reCapcha).
By spam accounts I mean 0 posts and links in profile pages.

I managed to ban some of them but they still show up in member list.
My questions:

1. What is the logic behind keeping spammer's accounts in active memberlist?
2. How can I manage simple task as listing users with 0 posts and deleting them at once? (some of this 11,500+ members are not banned but they have 0 posts)
3. How I can delete all banned accounts at once from banned user list?

 

[Blue]

Or maybe a usergroup option to show or hide that usergroup in the memberlist would be easier. So when you ban someone you could put them in the banned usergroup and be done with them.