This is partly because the editor commissions with an eye to
filling a set quota of pages but also because a key element of the quality control has taken place at the outset of the process: The editor has tried to choose an interesting topic and an author who can be expected to deliver an authoritative article.
Then the sucking is commenced by rotating said stick, upon which a rack of gauges swings into the picture: The right one shows the progress in
filling the current blood tank — each stage has a
set quota to fulfill — while the left shows the involuntary donor's shifting tolerance level.