On the basis that Peter McKay and Nigel Dumpster both fancied the job and were annoyed that the new kid wanted it. They took Peter Cook out to lunch to get him drunk in the hope that he'd get rid of Hislop. It backfired and Hislop became editor sacking both Dumpster and McKay.
Haha, I can imagine that giving Peter Cook the resolve to appoint Hislop.
I am actually slightly in awe of how not only has it flourished while most of print media has struggled, but with my proof-reading eye in (now with a monocle, obvs), there are precious few typos and gaffes in such a text-intensive publication, which I suspect is partly don to Hislop's oversight.
As I've mentioned before, I view my subscription as much as anything a subscription to their ferreting around the seedier side of politics and the sort of tenacity they show in various campaigns they doggedly stick to until everyone else catches up. IIRC, the only one they got really really wrong was in the MMR thing at the outset, but multiple times they have exposed various scandals that everyone else couldn't be bothered with - e.g. BRI children's cardiology, Post Office/Horizon, Lucy Letby (cotd p.94)