[ajnin]

The article also mentions that they have relatively little muscle mass, so maybe it is more rewarding to catch say a regular monkey rather than a sloth.

Evolutionary traits usually come with a tradeoff, and if a predator evolved to be able to catch sloths more easily it might make them less able to catch the juiciest prey, so overall it might be more worthwhile to focus on the other animals and leave sloths off the table, so to speak.