They are 100% not idiots (okay, maybe 99.9%), it’s just that from the outside the decision seems incomprehensible to us because we don’t have all the information. I am sure that there were serious internal factors and ETH was the cause of them, maybe it was a problem in the locker room (ETH's ego is well known), maybe it was some scandals with the management (he was not allowed to buy half of the Ajax team for astronomical amounts of money

). In some ways, ETH turned out to be so unacceptable that management took such a step, questionable from all sides.
Probably some things happened behind the curtains, but still, I would blame Bayer board for what happened. Things like Ten Hag ego was known before, it's first red flag. And I'm sure that they had discussions before signing contract about what they can do on transfer window. So, for me it's strange that they decided to sign contract and things went so wrong just after 2 rounds that only remaining option was to sack Ten Hag.