The insurers would be able to keep the costs in check, IF the employers were taken out of the equation. With employers, especially white collar ones, siphoning the healthy lives into their own separate insurance pools, the remaining pool of lives is costly to insure and thus only a very small number of insurers can afford to exist. If the pool of healthy lives was bigger to offset the cost of the sick lives, then multiple insurance companies can exist and compete on healthcare.gov to offer lower premiums which they can offer because they negotiated lower prices with providers.