Why are motorcycles bad on gas mileage?

The other day I was driving my friends 2014 Honda Fit. I noticed that it got about the same gas mileage as my 2011 Honda CBR 600RR.

How tuned the engine is mostly.

The Bike and Car have approx the same HP (~100). This means the bike's engine is tweaked to the max to get that power from 600 cc vs the cars 1300cc.

Tweak the cars engine to get ~250 hp, and be as fast as the bike, and see what sore of fuel economy you get then.

Now you can make a more economical bike, But you do this by building a much more sedate and economical engine, making maybe 50 hp from 600 cc. Still a good cruising bike at that power output, and should get get 2X the fuel economy of the 600RR

Apples and oranges. A Honda Fit is a cheap subcompact econo car. Your bike is a 160mph racing machine:
https://www.fuelly.com/car/honda/fit -- The majority of Honda Fits get 30-37 mpg.
https://www.fuelly.com/motorcycle/honda/cbr600_rr -- The majority of CBR600RRs get 36-46 mpg

You need to compare the Fit to an econo-bike, like a Vespa 250 -- and compare your racing bike with a car that can do 160 mph.

Often poor fuel economy is due to the rider's habits.

But you do not buy a supersport bike if you want fuel economy, you buy something like a Royal Enfield with efi which approaches 80-90mpg (but it is not that exhilarating reaching those giddy heights).

Well! I can throw a leg over my GSXR-1000 and get somewhere around 20 miles on a tank or somewhere around 150 miles… All depends on the mood I'm in.

You do the math!

My 1000 pound Harley gets 42 MPG. I'd love to have a car that does that well.

You CBR is high performance engine. It is not tuned to make great gas mileage, and you can expect between 30 and 40mpg depending on how you ride it.

Your Honda Fit engine is designed for economy and is capable of 40+mpg depending on how you drive it.

Motorcycle aerodynamics are horrible. It takes a lot more power per pound to push through the air at high speed than a typical car does. That's why motorcycles don't get 100mpg at 75mph.

It's not that the motorcycle is bad, it's that the car is very good. My 93 BMW 750 runs much cheaper than our six cylinder cars, but the are new 4 cylinder cars that run cheaper.

The honda fit is made for fuel economy and to be cheap running, the cbr is made for power and speed. Compare the economy car to an economy motorcycle and the car is going to use way more fuel. Considering the power of the bike compared to other bikes, to compare this to a car you need to compare it to a supercharged v8 or similar. When they make sportsbikes fuel economy is a very small bottom end of market factor, with a car like the honda fit getting good fuel economy is a selling point and a high priority goal for the engineers.

NO DARK SKIN!

Mpg is not what bikes were made for. At least not yours. Great mpg can be had by 250s and even the 125 grom would be sweet but that is not what the market wants.