Any reason’s fine. Many humans only do it because of social norms, not because they care about hygiene. See also, many humans only pretend to wash their hands after using a toilet.

I’d argue that the hygienic advantages of feces burying certainly help with the overall health of the species, even if it’s not the main reason. Might not even be a huge issue in nature due to the solitary nature of wild cats, but e.g. farm cats are often living in pretty close proximity to each other.