to stay loose and relaxed. and to lower the center of gravity. But mainly to stay loose and relaxed
your turn
my short answer is because of the range , they fight distance is farther than it used to be because of the removal of clinch and being able to push off , so there isnt a need to have your hands too high , its safer to keep them at mid level as to aid in blocking quik shots to the hogus ,as the fight gets closer the hands are then used to block head kicks ,,, also when attacking to close the distance , or combining kicks together having your hands lower makes you more fluid , too high hinders multiple motions .. as far as standing with their hands at their sides , that is a fighing technique just used to draw an attack from your opponent , some boxers do it as well ..
long answer ..... , i have been around long enough to see the whole tkd game change right before my eyes ,,, my friend in highschool was tkd national champion and i would go to watch him compete back in mid 1980s,, i started in 1985 , but not fully commited , until 1987 ,,,, tkd competitions back then resembled more of the karate you see now , side kicks , axe kicks , front kicks ect... , its nothing like what you see today ,, you could clinch as long as you didnt grasp , hold a little , push off and kick , all of these techniques have been taken away with rule changes , thus making fighters stand farther apart ,back then your hands had to be up because the threat of inside head kick was there,,, now the fighters have to gain ground first before they can reach the head , but still the body can be hit quit easily with a simple step over or sliding round kick , ect .. so the lower guard served as a blocking aid as well ,,,
"legs mahony" made a comment about people doing it because bruce lee did it ,,, thats not too far from he truth ,,, in the early 1990s a korean world champion destroyed everyone with a push kick / pop kick , and then after that you seen surfing come of age , everyone used a surfing style , and then guys started countering the surf and that changed , i was at WTF world championships in new york in early 1990s, there were two korean fighters , welter weight and heavy weight , i think ,, when they took the center of the ring they both stood upright with their hands holding their belts ,, not even in a fighting stance ,,,both of them were incredible counter fighters , every motion that was thrown at them was easily countered ,, they both went on to gold medals ,,, after that year , all of the sudden everyone turned into a super confident counter fighter ,,, people see something they like and a style they like and its being emulated ,,,if you take a top fighter from any club , you will find the majority of that club fighting and standing just like him ,,,when i competed i went through a phase of bending over with my hands on my knees and waiting for a counter , just because i saw a world champion doing it ,, lol,, some fighters used to pump their fist after a point and make such a big deal about it , thats gone now too ,, olympic rules have changed the whole martial art of tkd , it favors athletic , acrobatic kickers , spinning kicks score higher ect ... why do people stand like that .. the answer is because they have seen their favorite fighters stand like that and there is no reason to have your hands up to your face when one of the rules is no face punch ... i believe we are all correct in our responses , its just a bunch of different reasons...
as for wonderboy using that hands own low ,,, he uses his kicks to keep the oher guy out of punching range , so the face punch wasnt a threat to him , he also had an awareness to raise his guard when he was pressured or the guy got within punching range ...
ive attatched a video clip showing tkd from the 1980s , it has some traing and sparring in it ,,, hands are up ,,,clinching and pushing is allowed ,, i still have my dobok with the W.T.F. on the back lol this is the tkd i grew up with ...
1980s WTF korea national team training taekwondo - YouTube