I think he just saw how easy it would be to get away with it. He's married to someone else who has oversight on the business bank accounts. He wasn't being challenged and nobody wanted to even raise the issue.
About 10 years ago I was treasurer of the local playgroup, and joint signatory on the bank account with the chair. I had to approve all transfers he was making and countersign all the cheques. We're talking £20 for milk and a few quid for new felt tip pens, not close to half a million quid. And I was not married to the Chair!!
Bunch of fecking amateurs.