Why do the majority of modern Christians, if the Bible is trule, not follow the NT proscriptions for propriety

Because those "proscriptions" were designed for people 2000 years ago to follow. It is not practical for a woman to wear her hair down all the time, sometimes she must braid it to get it out of the way. And good luck convincing all those "Christian" women that gold, pearls, and expensive clothes are "sinful." You might as well try to convert all the no-nonsense Pagans and atheists to your "proscripted" religion.