It's just the perfect size for a cat to curl up in.
Yeah, but it's cold and usually damp, and there's a faucet that'll bump 'em in the noggin if they aren't careful.
But then, Halvah makes a lot of odd sleeping place choices. Like, for example, she doesn't really like to just sleep on the carpet, but if a paper bag gets left out, she'll sleep on that quite happily. Even if it's one too small for her to fit on it entirely. Looks silly.