He wanted to show that the character is dead in the first scene itself.
When Hrishikesh Mukherjee was making Anand, he informed his writer Gulzar to open the film in such a way that the audience knows in the first scene itself that Anand (played by Rajesh Khanna) is dead. He did not want the audience to be in a state of suspense till the end and keep guessing whether Anand will survive or not. By doing that Hrishikesh Mukherjee wanted to concentrate on the essence of the film on how Anand wants to live life fullest and make the best of the time he has.