Insurance companies generally have a loss ratio: a percentage of income from insurance policies they must pay out. In health insurance this percentage varies: it’s lower for individual plans, and higher for group plans. Most commonly it’s 80%.
If they pay out less, in many cases they have to return the difference to policy owners. (Not always though. Often with Medicaid, for example, this isn’t the case.)
This doesn’t mean that they have no reason to deny care, however. They want their health care costs as close to that bottom number as possible without going past it. If they spend, say, 83% rather than 80%, that will cost them billions. Denial of care is meant to get the margin as close to to loss ratio as possible.