When one of my kids was 4, they had an unexplained seizure. Hospital workup, whole nine yards, never recurred; it was probably a medication reaction. Years later we were denied coverage from all the private insurers over it (more accurately: we were denied any coverage for that child).

Similarly, insurers would as a matter of course exclude from coverage any woman with one of several extremely common conditions, including endometriosis, PCOS, fibroids, and adenomyosis.

Prior to Obamacare, insurers were free to deny coverage wholesale for these conditions. It would have been fucked up to extend coverage but exclude any neurological conditions from my kid, but the actual outcome was worse: they were under the law entitled to withhold any coverage.