There's absolutely nothing to gain from a boxer by going down though. The total opposite in fact. Short of claiming a low blow, but even then, why risk a count by throwing yourself on the floor?It's just how our cirulation and nerve system works.
Body hit knockouts in boxing is one of the clearest examples. They take the hit, stumble for a step, then the pain/shock hits and every sensory input to the brain goes: YOU ARE HURT, GET THE FUCK DOWN.
Boxers usually stumble down on their knees as they have a lot of willpower to stay up, unlike other sportsmen, but they almost never recover from that.
Footballers know laying on the floor could win them a free kick, penalty, red card advantage which is why they do it.
Worse, is that refs AND VaR miss so much, sometimes players HAVE to do it.