The problem with postmortems about things like this is that there is usually more than one way to look at it, and they can all be valid. For example, it's certainly true that if Republicans who supported cap-and-trade way back during the 2008 campaign had remained interested in working out a bill, then a bill would have passed. So (and wording this from the perspective of something having gone wrong) you can blame the Republicans who in some sense "should" have been at the table: Snowe, Collins, Gregg, LeMieux, Gramm, McCain, and a few others. Or you can blame the people who make Snowe, Collins, and the rest more concerned about primary challenges from the right than they are about anything else. Or you can blame the candidates who fell just short of giving the Dems a few more Senators over the last three election cycles, or the voters who didn't quite elect them. Or you can blame the filibuster. Or you can blame the structure of the Senate, which makes it likely that the Senate won't run by pure majority party rule (although it doesn't force the specific filibuster rules in effect today). Or you can blame Democrats such as Jay Rockefeller for putting the parochial interests of their states above the national interest and their party's platform. Or you can blame Harry Reid and other Senate leaders for not working out a deal with those Senators. Or you can blame Barack Obama for placing too low a priority on climate/energy.
All of those things are true! And they're not exactly competing explanations; they're all true, but just look at the issue from different perspectives.
I'll mainly repeat the point I've made before: it's worth noting that on a legislative time scale, cap-and-trade was really very, very, new, and most important laws tend to take a long time, often spanning several Congresses, to pass. Looking back...in 1992, global warming was a two-sentence throwaway at the end of the Democratic Party platform. If anything, it's even less prominent in 1996. In 2000, the Al Gore platform contained a fair amount of climate rhetoric -- but proposed almost no specific actions. No change in 2004: plenty of rhetoric, but only vague calls to action, mostly focusing on international agreements. No cap-and-trade, no carbon tax. So for Democrats, the idea that Congressional action is needed to limit carbon emissions as a core party principle only goes back to the 2008 campaign.
Matt Yglesias has a nice post up about the the regional complications of a carbon bill. What I'd add is that these are the sorts of things that can and do get worked out as bills move through the process. Think about the conflicts between rural and urban areas in health care legislation, for example. To look at the larger picture...legislating in the American, Madisonian system tends to be about interests. Until a bill actually starts moving through the legislative process, it's hard for supporters to know which interests they need to buy off, which they need to defeat, which they need to find compromises with, and what those compromises might be. No one knows how strong the opposition of nominally opposed groups might be (nor, for that matter, how strong the support of nominally supportive groups might be). No one knows which opposition groups can be bought off, nor what it would take to buy them off. No one knows which Senators are available with those potential compromises. Of course, proponents can guess, and the campaign tends to provide clues about these things, but nothing can really substitute for actually bringing a bill to the table that is headed for a committee mark-up.
Now, I'm not saying that all of this made climate/energy impossible to pass in this Congress. Plainly, Barack Obama and Congressional Democrats placed a lower priority on climate than they did on stimulus, health care, and the banking bill. If climate/energy had been the first thing out of the box in January 2009, it probably would have passed -- but stimulus gets delayed, with unknown but potentially dire consequences. If climate/energy is the big push in the spring and summer of 2009, well, perhaps it passes, perhaps not -- but health care probably doesn't. Lots of unknowns in any counterfactual speculation, but one certainly must accept that there were risks and trade-offs (as well as opportunities) involved in any other path. I also think that Kevin Drum has a good point that action really does involve some pain, and at least in my opinion it's understandable why Obama didn't want to stress policies that would involve additional sacrifice in the middle of an economic trauma.
Meanwhile, it seems to me that climate has now moved way up on the unfinished agenda of mainstream Democrats, which bodes well for some bill passing the next time that the Dems have unified control of Congress and the presidency. And it's by no means certain that GOP rejectionism is a permanent strategy; there are plenty of possible paths that could lead back to a significant minority of Republicans in Congress being willing to support climate legislation. Of course, should Republicans win back the House and hold it for a decade, then climate legislation might not happen for a long time. I'm certainly not going to make any predictions about election outcomes down the road. All I would say is that climate legislation got much, much farther in the 111th Congress than it ever had before; that Democratic activists will almost certainly place a much higher priority on the issue going forward than they have in the past; and that both of those are very good long-term predictors of successful action, if and when the Dems next get a chance to act.
[UPDATE: Please see important substantive comments from "Anonymous" below, who thinks that I got this one pretty wrong, and then my response].