Take the chip off your shoulder @Yogi-Bear.
It was NOT irrelevant, and my point was well made. I was in no way calling YOU stupid in that post.
However your triggered response to my suggestion that there are careless morons out and about on the road, and guidance has to be issued with such people in mind, coupled with the fact that I'm having to explain the difference between understeer and oversteer in greater detail as you couldn't grasp the concept when I made the point in a sentence, is evidence that you might not be the brightest bulb in the chandelier.
That's a YOU problem. 🤷♂️
I thought I'd explained myself pretty clearly here. Oh well, here goes again. Don't be replying to this post telling me you know all this already and don't need me to explain it at length, because that is literally what you just asked for.
Put simply, it's because of lift-off oversteer.
If a driver gets a bit out of shape in a car, they tend to brake, or at least lift off the throttle. This is well known, so most cars are set up to understeer if you go round a bend too fast.
When you do slow the car that has lost grip in understeer, there is a weight transfer, with more weight put onto the front tyres, and less weight on the back tyres.
As a result of this weight transfer, the front tyres grip more and the rear tyres grip less. (If you've ever ridden a bike, you should know all about weight transfer under braking.)
All being well, the car slows a bit, more weight transfers onto the understeering front tyres, which (fingers crossed) get more grip, and the driver makes it round the corner with the rear of the car obediently following the front. If this doesn't work, then the car continues the understeer and goes in a straight-ish line off the road.
This front grip gain and rear grip loss is exacerbated if you have tyres with more grip on the front, even before the weight transfer.
So if you have less grippy tyres on the back, when you get into your understeer situation, your most grippy tyres at the front have lost traction already, and as you slow the car while trying to go round the bend, you will initiate the weight transfer. At this time, you will lift vehicle weight off the back tyres onto the front tyres, and while the front tyres may regain grip, the combination of less grippy tyres at the back and less weight over those less grippy rear tyres at the rear can provoke oversteer. Oversteer is where the rear of the car does not obediently follow the front, but slides outwards turning the vehicle more than required. Such oversteer induced by slowing around a bend is called lift-off oversteer. Here's a fairly mild example of lift-off oversteer which the driver, who by the sound of the engine is fairly enthusiastic, discovers lift-off oversteer. While he quickly catches and corrects it, he ends up on the wrong side of the road facing oncoming traffic.
So to summarise:
Understeer sends you in a fairly predictable straight-ish line off the road, and is easy to correct by simply slowing down, which most people do instinctively without training.
Oversteer is less predictable, requires skill to catch and correct, and instinctive slowing down makes it worse.
The more grip you have at the rear, the less likely you are to oversteer when going round a bend too fast.
That is about as simple as I can make it.