At least here in Australia, any new bike you buy off a dealership has to meet the noise regulations, and under normal use they're almost as quiet as modern cars. The noisy ones you hear are all modified or old, perhaps both (a bike needs to be pre 1972 in Australia to be completely exempt from modern noise restrictions.)
There are even fully electric motorcycles available, but they're really not prime time "just go down to a dealer and buy one, and get it serviced everywhere" ready yet.
(Full disclosure, 2 or my 5 motorcycles have noisy exhausts. Not "hear from half a kilometer away" loud, but technically illegally loud and definitely loud enough that I take extra care arriving or departing home very late or early, out of respect for my neighbors. Interestingly for this discussion, the 3 bikes with quiet, factory stock, 100% road legal exhausts are all Japanese - in fact all Hondas. The noisy bikes are both Italian - a Ducati and a Cagiva.)
I'm just a little salty because I just went to two baseball games in kumamoto where my son was playing, and there were motorbikes somewhere, just doing laps I guess, for four hours straight. Everyone had to raise their voices when talking. I couldn't see any bikes, or even any well paved roads around the park. Just four hours straight of noise.
I will never understand why that is perfectly okay but talking loud in a restaurant will get you fired and ostracized. shrug cultural stuff I guess