Ann: Appointment of Experienced Lithium Executive MD, page-22

most companies will construct a deal to reduce notice period when it is 6 months or longer as it rarely serves the company well to hold a leader to being there when they have already decided to join another company. Expensive paying for that privilege, so they often agree to reduce it, save the money and move on.
As for why the wider search, i think it is good practice and it sends the right message to market. You don't want a scenario where the company gives roles to its inner sanctum without the proper DD or you tread a fine line towards a lifestyle company.