Lots of large employers are self insured, in that they pay the claims. So the risk there is anything beyond the out of pocket maximum, e.g., a heart attack pierces the OOPM and then runs up another $50K-$250K easily, depending on complexity.
Even if they are not self insured, most aim for an 80/20 or 70/30 split in total cost (where employer covers the larger portion). Given the potential total cost being allocated, is it a surprise employers are screening for health risks to help affect change?
Think of this too, the employer has employees for roughly 40% of their awake time. From a public health / population health perspective they are best positioned to positively impact health too.
Source: work in health insurance, population health. I have hands on experience with these types of programs.