Roberts voted how he did because health insurance companies are absolutely desperate for the money they will get from the mandate. All of the legitimacy arguments are bullshit, about 70% of Americans want Obamacare repealed. This is more similar to TARP than anything else: it is a massive corporate giveaway, opposed by the majority of the population, and passed over their dissent.
(Update: the post was later clarified to read that 70% of Americans want the mandate repealed, not Obamacare as a whole repealed -- which I think is a distinction without a difference, since I don't think that the unstated reasons that people have for opposing Obamacare are really separable from their opinion of the mandate.)
Do 70% of the population oppose Obamacare because it is "a massive corporate giveaway"? No. Articles like the one that I linked make an easy seque from opposition to "Opponents argue that such a mandate is an unconstitutional expansion of federal power, amounting to Congress ordering private citizens to buy a particular product." But that is the rationalized argument for public consumption. I would guess that real reasons for opposing Obamacare include "because Obama is black", "because I hate those leeches who want my money and I hope they die", "because there will be death panels", and, on the slightly more rational side, "because Obama is a Democrat". Maybe ten or fifteen percent are opposed to it because it's a massive corporate giveaway.
So there is opposition, yes -- but the idea that those who oppose it agree with each other isn't true. So, on the other side, do the elites agree? The idea that the decision is overdetermined -- that the insurance companies had a preferred outcome and that's why it happened that way -- doesn't appear to be true, as far as we know. The risible failure to cut-and-paste "concur" to/from "dissent" in the Supreme Court opinions makes it clear that the four more conservative judges thought that the decision was going to go another way until the last minute. If Roberts had voted the other way, all of the people who said that this was predetermined by elite interests would have still said the same thing. People could argue back and forth over whether it was straightforward elite interest, "enlightened" long-term elite interest, whether one set of elites edged out another, or so on. But the Occam's Razor explanation, at least to me, appears to be that Roberts decided as he did for basically unimportant personal reasons. Saying that the insurance industry is smart enough to figure out which decision is best for it, and capable enough to get this decision implemented, runs into the critical problem that our elites are not smart or capable. Every time we're able to observe what they do, they're doing stupid and medium-term self-destructive things.
How the system works is that none of the possible solutions on offer will be noxious to elites. Roberts could have decided to strike down the law and let people suffer under the current system, or to implement the massive corporate giveaway. But he couldn't decide that we'll have a single payer system. None of those solutions survive the gauntlet of elites at every stage of our politics. At the end, we get the arbitrary decision of a single person, whether it's how we're going to kill teenagers with drones or how we're going to keep bailing out banks, and none of our elites will be competent enough to control the exact form of what we end up with. But that won't really matter to them.
It may matter to us, however. Massive corporate giveaway or not, I can say that Romneycare is far superior to the private insurance that I had to buy directly in Massachusetts before it was created. I think that people on the left of the spectrum generally have good reason to prefer that the decision was made this way rather than being struck down. It's just that if we got something better than we might have otherwise, this time, it was because of the equivalent of a lucky die roll. And our political system is what makes this the best we can do again and again.