That's part of the problem; it's only legally required to be shown post-ACA.

https://www.irs.gov/affordable-care-act/form-w-2-reporting-o...

> The Affordable Care Act requires employers to report the cost of coverage under an employer-sponsored group health plan. Reporting the cost of health care coverage on the Form W-2 does not mean that the coverage is taxable. The value of the employer’s excludable contribution to health coverage continues to be excludable from an employee's income, and it is not taxable. This reporting is for informational purposes only and will provide employees useful and comparable consumer information on the cost of their health care coverage.

So, it went from "I pay $50/month for healthcare" to "my paycheck says they're taking $2k/month! what the fuck?!" in folks' minds.