It does have to be fairly high for the Media Matters/shareblue whatev - they can't really risk paid shills observing so much they get 'contaminated'.
Like their own observable tactical "outrage of the day", they move quickly onto the next thing, thinking rapid changes will keep 'their enemies' off their footing. They would change flunky-level people out just as quickly. Move them on to doing something else, like busing them to the next 'outrage' event or other assignment. Keeping them in a rotation of efforts (just like their rotation of outrages) so even their own flunkies are kept off-balance.
JIDF are zealots, they wouldn't need to change them out.
Same for the clowns, they don't have to change out for same reason as Brock babies, but they do change some of the more active ones, so that we can't get a fix on their writing styles and recognize them from one post to the next. That's another reason their posts are kept very short.