it extremely hard to balance the experience between young/old insurers. If the replacement plan doesn't offer something to encourage younger people to sign up I doubt you see them back in that market either
"Based in Louisville, Ky., Humana is not a major player in the individual exchanges and is among the national insurers, like Aetna and UnitedHealth Group, that have struggled to make money in the market. The company has steadily scaled back its presence, selling policies for 2017 in just 11 states. In early January, the company said the number of its customers buying coverage through the exchanges had dropped to about 150,000, a small fraction of the roughly 12 million individuals who initially signed up for coverage through the exchanges."
https://www.nytimes.com/2017/02/14/health/humana-plans-to-pull-out-of-obamacares-insurance-exchanges.html?_r=0