“And there was a time in this country when some of even the most Orthodox women didn’t cover their hair. It only really became accepted by all after frum refugees started coming here after WWII.”
And there was a time in this country when some of even the most Orthodox men and women wore shatnes. And then along came that pesky frum Holocaust refugee from Vienna after WWII, Joseph Rosenberger, and started Shatnes Labs in Williamsburg and it only then really became accepted by all to not wear Shatnes.
Like the m’doraisa prohibiting wearing Shatnes there’s also a m’doraisa prohibiting married women from going out with their hair uncovered. Even if in America, before the gedolim from Europe came to these shores and set things straight, there was widespread violations of these prohibitions.