The nuclear submarine thriller was cancelled by ABC this past weekend (November 17) alongside horror drama 666 Park Avenue.
"Our ratings had been on the cusp, or really below the cusp, for a few weeks now," Ryan said on Kevin Pollak's Chat Show. "[The cancellation] didn't come as a huge shock.
"It wasn't a huge shock, and yet still it's a disappointment. I would compare it to if you have a relative who becomes terminally ill. You know it's coming, and yet you still are shocked when it happens."
Ryan blamed the show's disappointing viewing figures on the "brutal time slot" of Thursday nights at 8/7c.
"We're up against Big Bang Theory, which is the No.1 comedy on TV; we're up against The X Factor; we're up against NFL games on the NFL Network that draw a lot of men - and men were liking our show," he explained.
The writer - who also created FX drama The Shield and short-lived Fox series The Chicago Code - added that ABC originally commissioned Last Resort as part of a desire to find a popular male-skewing drama.
"They thought it was a big, bold concept that would attract people," he said. "They were worried about putting something [on air] that was a little more normal, that it would get swamped and disappear."
Last Resort will air all 13 of its ordered episodes on ABC and on Sky1 in the UK.
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Watch Shawn Ryan's full interview on Kevin Pollak's Chat Show below: