It's because government is the god of liberalism. It may be a failed god, but it's all they have.
The worship of government is nothing new. In the ancient world, worshiping the emperor, or the pharoah, or the king, as an actual god was commonplace. During the middle ages, however, Christianity had reduced such worship to something called "divine right of kings" -- the king was revered because he was God's chosen leader, but he was no longer worshiped. This was progress.
However, the dictatorships of the 20th century pulled state worship out of history's dustbin and turned it into a fierce pageantry on a world-wide scope. Catch some of the films of parades in the old Soviet Union, with the belligerent likenesses of Lenin and Stalin hanging from every building; see the body of Lenin, preserved still, in a glass case. (He still looks good enough to share a stage with Joseph Biden.) Also: the Mao parades in China, the interminable Castro speeches in Cuba, and so on. There is something about government that titillates the fever swamps, particularly but not exclusively on the left, to a degree that is inexplicable as anything other than a manifestation of religious fervor. Such is its pull that it even turns rich liberal Americans into drooling sycophants. Examples abound. E.g., lefty journalists like John Reed (paid homage by Warren Beatty's in his movie, "Reds"), and Lincoln Steffens (who proclaimed, "I have seen the future and it works!"). E.g., Walter Duranty, the Pulizter Prize-winning New York Times reporter who helped the Soviets cover up Stalin's program of Ukrainian genocide. E.g., every Castro interview ever conducted by an American journalist. E.g., Ho Chi Minh posters in the 1970s. E.g., Che! T-shirts. Every left-wing dictator is some liberal's icon. They should make trading cards.
Why? Part of this is the problem of rejecting religion in the first place, or claiming it has no place in the public sphere. Nonsense. It will always be in the public sphere, the only choice we have is which form it takes. Human beings don't quit worshiping because they quit worshiping God. They will worship something -- if not brutal dictators, then their own wisdom, and politics is just the stage upon which vanity and egomania are played out on a large scale. Thomas Sowell often refers to these highly motivated busybodies as "the Anointed", a self-selecting class of folks who see it as their divine commission in life to bless the lives of the rest of us, a.k.a. "the Benighted", with their wisdom.
Just because the Anointed may not believe in Heaven doesn't mean they don't yearn for it. Such yearning takes the form of trying to create Heaven here on Earth -- to "immanentize the eschaton", in Eric Voegelin's eloquent phrase. The problem with making Heaven is that it requires superhuman wisdom and power. We must settle for Republicans and Democrats. Heaven help us.
But that doesn't stop the Anointed from trying. Problem is, there are too many institutions in the U.S. that stand in their way. The democracies in Europe have fewer checks and balances than our Constitution provides, and so the socialist agenda has been easier to implement over there. Our institutions are never so flawed as when they allow conservatives to be elected, or even to speak their minds. Hence, the hatred.