"No amount of counselling or compensation can give you back what you've lost and that's the bottom line of it," Rathband told ITV's Daybreak.
Former Scotland Yard commander John O'Connor said the consequences of Pc Rathband's injuries had been "too much for him to live with".
"If you can't live with the consequences of the injuries you've received then, you know, this is a way out for a lot of people.
"It's dreadfully sad, there's nothing that could be done, in my view.
"You get all the counselling, all the help that's available, all the back-up, but the reality is you've got to live with it and if you can't, that's what happens."
He said the police officer, who came under the media spotlight following the roundabout attack, had chosen to publicise his ordeal to help other wounded officers.
"The reality was, that was his choice and that was how he felt he could deal with the injuries he received," he said.
But he added: "He's a man that suffered these appalling injuries and at the end of the day, the consequences were too much for him to live with - he couldn't bear the consequences.
"We move on but the victims stay with their injuries and their trauma for ever."
A spokesman for the Blue Lamp Foundation said: "It is with great sadness that we learn of the death of David Rathband.
The charity he founded said Pc Rathband had struggled to cope since he suffered his injuries.
"Since being shot in July 2010, David struggled to come to terms with his horrific injuries and the traumatic effect they had on him and his family and friends.
"David's legacy will live on in the form of the Blue Lamp Foundation, which bears his name.
"The foundation was started by David to help emergency services personnel injured in the line of duty as the result of a criminal act.
"It was David's wish that those who found themselves in a similar position to him could receive the support that wasn't available to him at the time.
"David's family have asked that their privacy be respected at this time and they are allowed the time and space to reflect and grieve."