The simple reason is that race car engines typically aren't built with emissions in mind. There is no benefit using EGR other the emissions - unless the engine was designed with EGR in mind. Then you would have to consider that it may not have been designed with higher cylinder temperatures in mind. Higher temperatures can create problems with the piston, head, and cylinder wall. By running lower cylinder temperatures the designer may have gotten away with a piston design that may melt down under higher temperatures. Best be careful when playing around with this.
