What reason does Willy give that he can't work in New York?

At the beginning of the play Willy tells his wife that he can't work in New York because he's "the New England man."

They don't need me in New York. I'm the New England man. I'm vital in New England.

His wife says that the problem is that he is now sixty years old. Traveling to far-off states is beginning to wear him down. He was so tired on his most recent trip to Florida that he says he fell into a trance and drove off the road. Linda tells him that the problem is that Willy is just "too accommodating." If he really pushed the issue with the company, she is sure they would move him to a position closer to home. In some ways Willy agrees, but states that since his ex boss's son had taken over the company, his work has gone underappreciated.

If old man Wagner was alive I'd a been in charge of New York now! That man was a prince, he was a masterful man. But that boy of his, that Howard, he didn't appreciate. When I went north for the first time, the Wagner Company didn't know where New England was!

At the beginning of the play, Linda comments on Willy's increasing stress and difficulty traveling up and down the East Coast. She suggests to Willy that he ask his boss if he can work in New York instead of traveling to New England every week. Willy responds by telling his wife that his company doesn't need him in New York. He goes on to tell Linda that he is too valuable to the company as a traveling salesman and that they need him in New England. According to Willy, if his old boss were still alive he'd be running New York. He also tells Linda that before he joined the Wagner Company, they didn't do any business in New England. Later on in the play, Willy meets with his boss to inquire about a job closer to home in New York. Unfortunately, Howard tells Willy that he doesn't have a single job for him in the city. Willy then begins to ramble, and Howard eventually fires him.