This. It's like the "you MUST sanitize the bottles!" - which advice is based on the assumption that they are not being VIGOROUSLY SCRUBBED in very warm soapy water until absolutely all trace of milk is gone and then air-dried.

Because you can't assume that, but if you insist everybody boils them for ten minutes on a regular basis, it doesn't matter if the cleaning isn't Perfect, because the relevant microbes have been killed off anyway. Same with the other stuff.