It's most likely the lawyers AND the fact that the government makes manufacturers average the fuel mileage ratings of all the bikes in their fleet to see if they "comply" with current efficiency standards (weather possible or not) .
So the manufacturer has to print the (proper shift point) to make it official for the record.
I'm sure the printed shift points correlate to some "best" efficiency test.
It has ZERO to do with how they really expect the bike to be ridden in any real world circumstance.
I've never seen CAFE requirements or regulations for motorcycles.
Best performance in the economy area would come about if you ran the bike at the bsfc sweet spot. From what I remember about the shift points in the manual, there are lugging type shift points, and would not be anywhere near the bsfc sweet spot for any operating condition.
So I doubt very much if government regulation has anything to do with this ... and I lay the blame entirely on the lawyers who are focused on CYA instructions that would make it hard to get in trouble due to your right wrist.
Edit: CAFE stands for corporate average fuel economy, and it is specified for the manufacturers of passenger cars and light trucks. The current administration set the goal that we will have a CAFE standard of 54.5 by 2025.
There are no current vehicles that meet this standard.
There are electric vehicles that achieve higher nominal values in the form of MPGe, but the e is the kicker.
The e stands for equivalent. They do a pretty reasonable scientific analysis of the equivalent mpg from the power plant to the in home charging station, but then they divide the whole mess by a factor of .15. The .15 is a term that is included to account for the value of electric vehicles to the society. The effect of diving by .15 is that MPGe figures are about 6 times larger than their honest mpg equivalents. So when you see that the electric car has an MPGe of 120, it's actually more like 20 mpg when reflected back to the power plant where fuel was burned in order to create the electricity that eventually was used to charge the car's battery.
Sigh....