I agree that BMI is not a very good tool for all and is skewed so most people are overweight.
That said, this arose a few years ago as a cost saving measure. Health insurance is about group risk. There is no obligation for the company to insure anyone, right now anyway.
And there is no magic “insurance company” money to pay for things. Its self insurance. The company and us pay for everything.
Thats essentially true for all employers, self insured or not.
As a workers comp casemanager, I enjoyed working with the companies that were self-insured-the employees were realistic in their expectations, mindful of safety rules and workers comp cheaters were few and far between.