They are. Try to buy insurance outside of open enrollment without a qualifying life event; you can, but only from insurers who underwrite against preexisting conditions. That's for the same reason: because otherwise, people would just forego insurance until they needed it.
Wouldn't that be the rational approach? Otherwise, insurance is still a tax on young and fit to finance the medical treatment of the old and unfit. At which point it's socialism but less efficient.
It's like if your car insurance covered getting a new one if the old one is at EOL. Imagine a cost of that and also the level of willingness to participate by the ones who just bought their first car with cash.
Congratulations to the US people for discovering a model less efficient than socialism.
You're spot on, but it's even worse than that - since these pools are administered/owned by private companies, their incentive is to collect money from people while they're young and healthy, only to push them out once they're no longer young and healthy!
I'd say that any sensible reform must intrinsically be based on some combination of a whole-society pool and individual payers. These highly broken approaches of provider networks and custom negotiated pricing need to be completely eliminated. Insurance should then be an optional thing only meant for people who prefer to financialize their life (like pet insurance), and should cover a formulaic amount of any bill from any licensed provider.
At the youngest adult ages that contribute most to premium reductions productivity is largely a function of investment of the parent, so it may be even more dire than you phrase it. Its effectively a transfer of wealth of investment from parents who have just spent 18 years producing a taxpayer to unhealthy non-parents who comparatively took little of the risk and cost but equally gobble up gains to the risk pool. Another words, it is a regressive tax that rewards goading others into taking on parental responsibilities while taking on none yourself.