Speaking at the Los Angeles Festival of Books, the pair said that they would not have pushed ahead with the controversial miniseries without the proper talent involved.
They also said that Alan Moore should have read his Watchmen contract more carefully.
"We would not have gone forward if we didn't think the talent was available to be perfectly honest," DiDio said of the seven limited series. "That's actually one of the things that slowed us down.
"And the talent didn't want to participate unless they felt they had a key story to tell. Darwyn Cooke was one of the first people asked and he turned me down because he didn't know what to do with it. And then a year later he comes back and he knew how to make the story work. Then we're off to the races."
Lee said that the success of Watchmen outside of the usual comics readership made the prequels an irresistible opportunity to expand the publisher's business.
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The pair also addressed Watchmen creator Moore's criticism of the new project.
"This is not a situation where we have taken things from Alan," said Lee. "He signed an agreement and yet he said, 'I didn't read the contract.' I can't force him to read his contract.
"It's not as clear-cut as people want to make it seem... It's not a situation where we're using the characters and Alan's not being compensated. For everything that's been done for Watchmen from the books to the movie, money has gone his way. The right amount that he deserves based on the contract.
"So we have honoured that part of the agreement. It is something that can definitely be debated but to say that there is clearly one side that is right, I will dispute that."
Before Watchmen will launch in June.
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