That's just how insurance stays solvent. Imagine if car companies sold you car insurance after you'd gotten in a car crash. It wouldn't really be insurance then, would it? You'd just be paying them to pay your bills, which isn't exactly a sustainable business model.
Not really the case - insurance mainly works when the majority of the people paying the premiums (and rarely using the service) covers the costs of the few that need expensive services. In the car analogy: the law mandates that you carry auto liability insurance, which ends up lowering the costs for everyone. This is what the ACA had at its core.