Because his estate had to go through probate.
Probate is the process by which courts verify that wills are valid.
In most states, it lasts a minimum of one year, and it can take much longer. During probate, assets are frozen and not available to heirs. This gives creditors time to get paid and relatives time to challenge the will. The more challenges, the greater the delays. Therefore, avoid naming a bank or lawyer to serve as executor of your will.