We should get that global cycling body to force all nations to adopt the same standard. Oh, wait....
You can find various alleged "reasons" for why different countries take different approaches, but the reality is that nobody really knows the answer.
In the USA, consumer safety rules mandate the right-rear/left-front layout, and getting this 'wrong' has resulted in safety recalls (and probably some lawsuits...):
Hand lever location. The rear brake shall be actuated by a control located on the right handlebar and the front brake shall be actuated by a control located on the left handlebar. The left-hand/right-hand locations may be reversed in accordance with an individual customer order.
I'm just happy to live in a country sensible enough to put the front-brake lever in the same place on both bicycles and motorcycles...
There are factual reasons as to why levers are specified in a specific manner on a bike or a motorcycle; none of which is worth wasting time one since none of it matters.
You are responsible for being familiar the operation of anything you are in control of. Injury or death can result to you or others just because tou want to have fun, or for some other low priority reason. Anybody here rent a car and read the owner's manual; or even on your own vehicle? Be honest!
I have seen severe injuries to those who think they know something when in fact they do not.
If you use something that is not yours ask about, inspect it, and read about it.
If you lend something, make sure the operator is knowledgeable about YOUR equipment! Tell them antrhing that is odd (whether factory, or custom modification).
This is the only reason at present why I have my rear brake lever on the right side (USA): when I am cycling in city, suburban, or high traffic areas I need to be able to convey in a visible manner hand signals to those behind, and if needing to brake simultaneously while signalling with my left hand, I prefer the better control of braking one-handed if the braking is on the rear wheel and not the front. When I was in Virgin Islands I reversed it. If I did not use hand signals it would not matter to me, but still in my interest to inform anyone borrowing my bike (would never happen except in a life or death situation) of my set up to avoid damaging it as I do not care about the rider as much as I care about my transportation if they are not intelligent enough to educate themselves for their own preservation.
Location: Parañaque, Philippines
this was news to me too a couple of years ago, is it just in the UK and Australia where front = right and rear = left? and then rest of the world is front = left and rear = right?
Location: Noosaville, Sunshine Coast, Australia
The only thing I can think of for a reason is hand signals/indication...lifting a hand off to let cars know which way we're going...But again, that's marginal as to which brake you prefer to use in relation to the hand/arm you're indicating your next turn.
Bit confusing really...🤔