244) Out of thousands if not millions of isolated patches of grass on Earth, Visser Three has to habitually choose spots that the Animorphs can locate or get easy access to.
245) Also, even though Visser Three has an elite guard around him at all times and there are crucial pieces of information that not all lower level Yeerks have access to, his feeding grounds are apparently not on that list. I mean, someone might need him to handle a customer complaint or something.