I have a theory on why cookies at various academic department sponsored events tend to be low quality in general, but not completely inedible.
If the cookies are very good, the first few people who arrive at the event have a feast of cookies, and there are only a few crumbs left for the rest. To compensate, the event needs to have many more cookies and word gets out, so that in the end it costs too much to keep the quality up.
If the cookies are too bad, nobody shows up and you end up with no attendees to the event. Or if people show up, it becomes a matter of nature to have complains on the quality of the cookies, with ensuing food fights and/or bad joke contests.
The happy medium are cookies that are good enough to be an incentive to students who go for the free food, but bad enough so that nobody really wants to eat more than their share. I’m sure this general lesson applies to a lot of other social activities.
I have a lot of circumstantial evidence supporting my case.