Speaking to CVG, lead designer at Bizarre, Ged Talbot, said the company would have needed to "(come up with) something that was big" to justify making another addition to the popular XBOX-exclusive racing franchise.
"By the time we got to PGR4 I certainly felt that the time was right to move on and do different things. I loved what we did with PGR and MSR. We put a lot of time into it and year-on-year we did everything we could to try and improve it.
"We could've done another one but equally the challenge to do something else with a different appeal - a much broader appeal - was too big to pass up."
He went on to discuss Bizarre's split from Microsoft and that the decision to stop future PGR from being developed was made before the buyout from Activision.
"I think after we did bikes for PGR4 we would've struggled to find something that was that big to put in the game. We were extremely lucky with the way things went with Microsoft. Some of our SKUs were launch titles so we were able to make graphical explosions and that was our platform for making the game. We debuted Xbox Live.
"But as time went on those big chunks of features were getting harder to come by and we needed to keep reinvigorating the title. Any more just would've been pushing it I think. For us it was a breath of fresh air to do something different."