Reasons why ritual laws for Moses could not have anything to do with personal hygiene:
1. In Acts, when God asked Peter to eat the unclean animals, could He be interpreted as asking Peter to eat unhygienic food? Also Jesus deliberately touched lepers and let the hemorrhaged woman touch Him, was He to be interpreted as doing something unhygienic?
2. For leprosy, in Leviticus 13:13, when a person is fully leper, he is clean. This wouldn’t be the case if leprosy is personally unhygienic.
3. In Leviticus, when an animal is considered to be clean or unclean, Moses uses the distinction of whether it splits hoof and chews cud at the same time or not; and between whether it has scales and fins and lives in the seas at the same time or not; etc. There is no mention to personal hygiene at all. Plus according to the Law, there aren’t actually many animals which are not unclean, but Moses didn’t make the list of those permissible meat, he tries to distinguish between the animal being a mixed species and not.
4. Why would holiness have anything to do with personal hygiene?