Eh, I've seen a few costumes here and there that are at least close to that sort of kigurumi, if not actually so.

The reason though why it gets a weird rep is because people associate it with the real otaku who have some sort of fetish for the characters and the kigurumi is just taking it to another level. (like, a step beyond fullsize body pillows and just generic crossplay, sort of thing)

Some cosplayers do that sort of thing just for the sake of cosplaying, but probably because of making the masks and such more prefer just to stick with the fabric and wigs.