Why did it take Hollywood so long to make a movie about Liberace and his boy toy Scott Thorson? Oh, never mind. At least director Steven Soderbergh saw the potential in the saucy story, and got Oscar winners Michael Douglas and Matt Damon to star. (In “Behind the Candelabra,” which premieres on HBO May 26, Douglas plays the preposterous piano man and Damon channels his much-younger lover.) In the new issue of “Entertainment Weekly,” the two actors reveal they’d talked for years about making the movie. Damon says Soderbergh gave him a copy of Thorson’s book in 2007 and said: “ ‘You and Michael Douglas.’ And I say, ‘Get the [expletive] out. What are you talking about?’ But I went home and read the book, and the next day I was like, ‘What is this going to be?’ He said he had Richard LaGravenese to write it, and I said, ‘I’m in. Whatever it is, it’s going to be great.’ ” It also sounds like we’re going to see a lot of Damon’s derrière because the actor got regular spray tans on his bum during filming. Says Douglas: “I don’t know any actors of Matt’s caliber who would be willing to take on the part of Scott. I thought it was really courageous. It just shows you the width and breadth of his career. But I don’t think at my prime at his age I would’ve had the courage to take this part on.”