An Auckland university physics student emailed her lecturer, two weeks into her physics course, with a proposition: the lecturer and his wife should join her for an adventure in Bali.
A lecturer receiving this kind of email has to forward it on to the boss.
Departmental lore at Canterbury had it that, a long time ago, a former lecturer there had received a similar proposition. He told her that while such an adventure would certainly be enjoyable, she would afterwards be able to hold him to ransom for the present discounted value of his lifetime earnings - and no amount of present enjoyment could compensate for that.
Back to the current case:
That's one layer to the problem.
But add in the Dean's perception. Suppose that the lecturer never replied but the email came to light later on. If the Dean believed there could have been a sex-for-grades thing, whether or not anything transpired, it's risky for the lecturer. Can you prove that you didn't have some non-email conversation later on that led to a sex-for-grades thing? Hard to do. Safest course then for the lecturer is to forward on the email immediately to demonstrate innocence.
Good students of game theory would then not make any sincere proposition until it were safe to do so, but that's difficult where you never know who will be your lecturer in a subsequent year or your supervisor.
Lecturers not having received such requests should take it as testament to the quality of their teaching of game theory.