Diesel has no octane limitation? Do you know what you're talking about? "Octane" in gasoline serves to minimize the risk of autoignition. A diesel engine operates without spark plugs but with a very high compression ratios (which is one reason they can be more efficient) to intentioanally autoignite the fuel / air. Diesel is not rated on octane at all, but an equivalent octane rating would actually be very low.
Each type of fuel has it's advantages and disadvantages. I happen to like diesel and wish more vehicles used it in the states. And as far as racing goes, each series has its own rules governing engine limits for different engine types, specifically to try level the playing field (or advantage someone if they want). This is currently the case, some claim, with the LeMans series and the diesels. Teams chose whatever they think they can work with most effectively.