Why does hair fall out more when is oily/dirty?

Oily hair or uncleaned scalp does not cause hair loss. Genetic trait is the cause of male pattern hair loss.  You may notice more hair loss on certain days and that may be normal.

A normal head of hair can shed up to 100 hairs per day.If you only wash your hair 1 x per week then you will notice more loss upon shampooing that 1 time.Does that make sense?

This never happens. Think about all of the homeless men on skid row who have not had a bath for months and have a full head of hair. Dirt and oils do not cause hair loss