No one said you need to do it every single day, but as soon as you feel the need to, if your brain is working properly.
There is nothing more disgusting than entering a small room (a store, for example) and the guy next to you is dressed like he spent 2 years out in the desert, and stinks like someone smeared him with cow feces.
Is it so hard to stand up in the morning, brush your bloody teeth and take a damn shower if you have to go outside and be next to people? Well, that would be too much to expect, considering some people don't even clean their houses on a regular basis.