ACA put the nail in the coffin of many of those plans, but they were already severely wounded by the states they operated in before ACA.
I spent many years in group plans sponsored by professional orgs. In the earliest years, the insurance companies had free reign to set premiums based on the history of claims by the org members in the plan.
In Massachusetts, the state regulators when faced by rising premiums in individual plans limited and then eliminated the ability of insurers to use the history of claims in the plan to set premiums requiring that history be combined with individual plans to help lower their cost.
Over the same period, there was an increase in mandated coverages, similar to ACA mandates. One year our premiums rose 20% with no significant increase in the claims history of our plan.
Regulators choose winners and losers based on their opinion of what is the public good. Whether you agree they have succeeded in their assessment of the public good is often colored by whether you have won or lost.