Motorcycles have gone through many evolutions through the years, especially where controls are concerned. The throttle was a lever located on the fuel tank for many years on most models. The first Sportsters had the shifter on the right foot for track racing.
The US DOT standardized motorcycle controls and displays in the early 70's.
Most European bikes had the foot shifter on the right side. Ossa was an exception. Bultaco had the shift pattern reversed on the Metralla due to the link set up - one up four down. The Triumphs and BSAs along with most all other British bikes had the right side shift pedal from the thirties on up. I rode a 38 BSA 500 with the right side shift - a bit clunkier than my Bultacos no doubt, but very entertaining.
The thing that happened relative to the standardization had more to due with the huge influx and influence of the Japanese manufacturers who's machines virtually all had left side shifts. Some had a right side stub for conversion, but very few. So when it came time to standardize, it was the majority rule situation.
There were some weirdies there in the left side shift bikes from Japan too. There were the upside down patterns, now called roadrace patterns, where first is up. But they had some complications in neutral placement in some too. It could be N then up for 1-2-3-4-5 and there might have been some N then down for 1-2-3 or so.
The most notorious, the most insideous was the infamous rotational pattern from Bridgestone and maybe some others. It went N-1-2-3-4-N-1-2-3-4-N-1-2-3-4 ad infinitum. Yes, you are reading this right, you could shift through 4th and if, not knowing what gear you were in, you went for another gear you'd hit neutral, if you thought you missed a gear and shifted again you'd be screaming the guts out of the engine back in first.
Talk about a dangerous pattern!
Personally I liked the right side shift/left side clutch... but then again I liked Bultacos and flat tracking.