Your assumption is wrong. The Affordable Care Act (Obamacare) imposed a minimum medical loss ratio on health plans. If they pay out less than that on claims then the excess is refunded to customers.
https://www.cms.gov/marketplace/private-health-insurance/med...
Most large employers now have self-funded health plans where they bear most of the financial risk and indirectly pay most of your claims. Thus HR departments have a major incentive to switch carriers to lower costs. Regence probably negotiated lower rates with their network providers.
But if you really think it's a scam then you're free to opt out of coverage during open enrollment.
