There are two possible ways to look at this. For one, Willie's dream of hundreds of buyers coming to his funeral, celebrating his life, comes to the end we all knew it would come to. No one comes; he is buried by his family and a couple friends. It's unclear whether Linda knew this was coming; she laments that no one is there, as though she somehow expected them to come. If there were ever any suspicion that Willie's dream may have had some substance to it, it ends at the Requiem.
The other thing that we are having a Requiem for is an idea, in a way Willie's idea, that the business world works on a handshake, that personality can carry the day, that being "well-liked" will get it done. Bernard is the new man; Bernard has no personality and Bernard is successful. This is (may be?) a new world, and it works on new principles. In Willie's old world, "a man is not a piece of fruit." In our world, he certainly is. You can eat the fruit and throw away the peel. Giant corporations, symbolized by the apartment houses that surround Willie's "world," relate to people differently than the corner store that might loan you money is you were short.
So we say goodbye to a man and to an idea ... all in one short act.
It provides a very bittersweet closure, in that during the funeral, Linda tells Willy that they were almost free and clear. This is referring to the fact that financially, it was almost to the point that they could stop struggling to make ends meet. They had just made the last mortage payment, and things were starting to look up. It just goes to show that Willy killed himself needlessly for the insurance money.
The funeral was also very lightly attended, with only the family really attending. After all those years of thinking he had hordes of friends, Miller shows that he had acquired no true friends except for perhaps Charlie, who looked after him knowing he was less than stable.
Perhaps the message here is that people do things needlessly due to the demands of the working world. Willy was chewed up, spit out, and used up for all that he had of value to his employers. Miller emphasizes this when Willy compares himself to an orange, saying you can't eat the flesh and throw away the peel. It was truly a telling ending, leaving the reader with a feeling of disappointment.