If we’re only relying on info from ROTJ and disregarding anything else that’s “canon”, I think it’s much more likely that what is said about the Sarlacc in the film is mostly false, comprised of legend and rumor. It’s not like there’s any reason to open it up and actually see how long it takes to be digested, so why not hype it up a bit? Surely it would make watching an execution-by-Sarlacc much more entertaining…
Watching others suffer seems to be Jabba’s favorite pastime, so why not turn it up to 11?