If you look at the health insurance system that existed in the past this was not as big of a problem. Initially you had most health insurance being provided by mutuals where they did not have concepts like preexisting conditions. But what happened was these non-profits were soon getting dominated by for-profit health insurers. Not because these private insurers were more efficient, but rather because they invented concepts like preexisting conditions and did a lot to limit the pool of people they insured. This let them offer lower prices and seem like a better deal until you got sick and they upped your rates or got rid of you all together.
This got an order of magnitude worse as some of these private insurers became publicly traded companies. Not only did going public give them more capital to work with to further undercut competitors, but it also created a necessity of every increasing profits on a quarterly basis. That means they have to continually find ways to screw the insured.
So no, it wasn't always this way, but it definitely is now.