I'd say its because blonde hair (in korea) at least is seen as more "exotic", "new" and "attractive" rather then black hair which literally every korean has. It's also much more eye-catching than anything, imagine coming to school expecting to see the same normal people and suddenly theres a new student who has blonde hair... You'd obviously be looking at them, right? Especially since over there is some VERY strict hair-dye rules in schools (half of them always banning it) so you almost never see it.
I also wouldn't say its the race that comes from it either, but it also can be in certain times. In here, its more about it being foreign and catchy that makes you want to look more into it. If you saw a black, indian, japanese, whatever race with blonde hair you'd obviously be very interested and might look at them more than normal... But with normal, ordinary black (which is not even black, just dark brown???) You'd still look at them but not be as jnterested as them having a foreign hair color.
Its also why red, blue, pink, white and etc hair colors catch our attention so much. You dont see them at all in normal spaces so you'd be noticing it even more when they're in a room with you. sorry for yapping LMAO OMG
Just starting to read this and the baby is obviously very cute and pretty/handsome while growing up. But as an Asian, I do question why he can't be a cute, pretty handsome black haired kid, why does it need to be blond? One might say i see too much into it, but it is little things like that, that we associate blond hair (and the race with it) as more pretty/handsome than black hair.