Why is it ok to be incompetent when you are an executive ?

This sounds less like a question and more like a vent about an unacceptably incompetent executive being criminally idiotic, which is way too bloody common. (and to answer your question - ego, entitlement, a sick system, too much apathy for anyone to stick their neck out and do something about it - take your pick)

It's not.
They just get away with it because they're able to shift blame.
But eventually it catches up.

They can delegate out all the work and take all the credit.Many executives think they are amazing when they are terrible.One particular case is Fred"the shred"who was the biggest single person responsible for the near collapse of the UK banking system on 7 October 2008.The government bail out cost at least a trillion pounds of taxpayers money.

Thats just how things are 😂 no common sence.