It's was pretty easy to predict: allowing enrollment after a diagnosis was politically popular but a terrible economic disincentive to not buy insurance (because at that point, it isn't insurance -- it's a subscription plan for your treatments).
The young and healthy needed to enroll for the economics to work, but the individual mandate was delayed for years -- because coercion isn't popular politically, and there was a reelection to win in 2012. Without the coercion, why would a 20-something buy insurance?
So begins the death spiral. The only thing that can save it is very high penalties for failing to get insurance on the individual marketplace. This would be politically disastrous -- "we know the plans are expensive, but it will be even more expensive to not get one!" isn't a great selling point.
It's not only that you have to pay up so that others may wait until they're sick -- you have to buy a plan that covers things you don't need. I have to pay for all sorts of treatments I'll never use -- addiction counseling, prenatal care (I'm a man), etc. -- because it was considered unfair that I should pay less for consuming less (why this argument doesn't transfer to auto insurance, where men pay higher rates, I don't know).
I know liberals are going to argue "that's why you need to take the market out of it and have single payer." It's a consistent argument only if you believe that you'd be better off with single payer. Some people would be; I know I wouldn't be. I'd end up paying even more for everyone else who isn't paying.
But, politically, that's dead on arrival. Democrats just voted to abolish the cadillac tax. Everyone knows the ACA is an albatross on the Democrats' neck. The sorts of anecdotes in this thread are all over the place. "We just didn't go far enough, try single payer" is not going to win the day anytime soon.
If a Republican wins the presidency, we'll see a full repeal of the entire thing (Dems will not filibuster if they know what's good for them). If a Democrat wins, we'll see gradual repeal, marketed as tweaks and improvements.
Personally, I'm fine with a strong subsidized public option for the truly indigent (oh wait, I just invented Medicare). After that, let the market bring costs down by removing regulations. It's no coincidence that laser eye surgery, teeth whitening, cosmetic surgery is all generally affordable -- markets and competition have formed.
A good market would be one where you paid your doctor out of pocket for recurring, predictable costs and then bought insurance from a private company in order to guard against unforeseen catastrophes -- kind of like how your auto insurance policy doesn't pay for oil changes and car washes.
And what if someone is irresponsible and didn't qualify for Medicare but also didn't buy insurance? What happens if they get cancer? I hope they have family and friends to bail them out. It would be great for charities to lend a hand. I don't think the role of government is to take care of you, because it isn't the government taking care of you. It's the government coercing others to take care of you, against their will. It is not charitable to hold a doctor at gunpoint and force him to perform a surgery. So for everyone who believes that healthcare is a "right," I expect that you're freely giving away your excess time and money away? Or do you just expect others to?
I'm already paying someone else's medical bills -- I can calculate how much I give to Medicare each year, it's more than enough for someone else in this country to see a doctor for the entire year. I'm also paying way more than I should for my family's insurance plan because I'm indirectly subsidizing others. I wonder how many people are getting free healthcare on my dime, and what excuses they have for not being able to afford it on their own. I'm a little tired of being told how great it would be if I just paid a little more and others paid a little less.