Unless someone's teeth are horrendously bad & they have raging halitosis then I don't really get s teeth ick, slightly yellow enamel is meant to be stronger than white so I believe? Lots of folk struggle to put food on the table, let alone afford dentists charges at the moment, white teeth is not of life threatening importance to many just now.
Like many things we have been conditioned to accept fake as the norm. Perfectly straight white teeth are not normal, they are straight out of a money making dentists chair. I am amazed at how many people will destroy their own natural teeth to have perfect cosmetic ones. I use to love quirky teeth everyone's smile different from the next person.
As you say yellowish teeth are strong teeth, Also teeth with bright white patches are because of too much fluoride.
My own ick is perfection. I love the unusual and quirky.