It's because the political right completely controls the debate and vocabulary down there, plus a huge proportion of the media. They've managed to convince Americans that "liberal" is an insult or a slur, like "f*g" or "retard", instead of the value-neutral description of a specific political position.
If I could hazard a guess, I'd say there are way more "liberals" down there than people who are willing to utter the words "I am a political liberal". You can get a better read on the situation by looking at Americans' opinions on individual issues. Should pot be legal? Most Americans say yes. Abortion? Again, most say yes. Do Americans want universal health care? Yep. Would they prefer diplomacy to war? Absolutely. Are they against discrimination based on gender, sexuality or race? They sure are. Will they find a way to believe all these things and still call themselves "conservative" instead of "liberal" - you bet they will! Nobody wants to admit to being a faggy moron.
That is part of the story, but the primary reason why conservatives have more media clout than liberals is because the filthy rich began to see liberalism as something between neutral and hostile to their interests in accumulating more wealth and power for themselves. The infamous Powell Memo, written by future Supreme Court appointee and corporate attorney of the time - Lewis Powell, layed out the game plan for the conservative takeover: where he told the oligarchs to put their money where their mouths are and fund conservative think tanks...to be followed by swamping the media with their experts, the takeover of economics departments in the universities, and create right wing conservative media. The right wing conservatives amalgamated with the majority of conservative religious leaders in the 70's and began the propaganda war at least a decade before the liberal establishment became aware that they were under attack - the election of Ronald Reagan as president
In response, the Democratic Party and media liberals moved to the right, and abandoned the institutions that maintained liberalism in America: unions, state universities, liberal churches, and a free press. Professional liberals caved, and started calling themselves moderates or centrists, and have kept giving up ground ever since...and yes that especially includes Obama!
Some books I've read in the last 10 years, like Thomas Frank's "What's The Matter With Kansas" show how successfully the right has been at hijacking populism, so that, in a state like Kansas, the loyal supporters of a long line of Republican legislators, vote against their own economic interests to support God and Country...or vote against abortion or whatever trumped up social issue the Republicans are running on today. The banking meltdown in 2008 should have been the end of supply side economics, the Republican Party, and ushered in the kind of banking reform that FDR instituted back in 1933.
But Barack Obama was no FDR...in fact he was brought in by the investment bankers; so his decision to follow through with Bush's Wall Street Bailout, rather than to support the millions who lost their life's savings to liar loans and other mortgage scams, took away an easy opportunity to build the liberal populist base. In a nutshell, there are liberals in America, and a growing number of people who have given up on liberalism and moved further left! But they have to endure an onslaught of propaganda every time they turn on their radio or TV, and no longer have a political party that represents their interests. Both the Dems and the Repubs are merely two sides of the corporate party that represents the interests of the people with the money to fund campaigns and reward politicians when they are safely out of office.
Another issue Americans are going to have to ask themselves is:
how much freedom do we really have today? Just asking...because it doesn't escape the notice of any outside observers that populist movements of the right, like the tea party demonstrations are promoted and given wide audience in the media, while peace demonstrations, anti-pipeline demonstrations, the Occupy movements etc., get almost no notice in the media until there are mass arrests. On that subject, worth noting how the Homeland Security collaborated with local police forces to shut down all of the demonstrations. The response from law enforcement to any movements on the left is a lot more extreme than justified, whereas a right wing demonstration can be easily coopted by the oligarchs.
