Office politics, i.e. power plays. Having information and deciding who gets it is a massively powerful position in an office. So Senior Manager Butt Dickdong who otherwise has nothing to do with the thing has to sign off on the slides because it allows him information before the rest and the chance to torpedo it or give some favours away. Of course having nothing to do with it, Butt doesn't really know anything about it and as such needs constant explanation because he thinks if the slides are for an egyptian client you should use Papyrus font like they do over there.

It is also why these things are so hard to get rid off, it'd mix up power structures. I don't think most of the people doing it are consciously aware of it in the Machiavellan sense but they do know it internally. Also partly why consultants are so common now, it gives the C-Level Suite an excuse to say "oh this is just objectively better" to Butt who can't really argue against it. Now of course consultants also design the worst shit known to man because they depend on you coming back to them because otherwise they'd slowly work themselves out of a job, which they are accutely aware of and trained on.