Why single primary key is better than composite keys?

Question

Why is the rejection of composite keys in favor of all tables using a single primary key named id? Cause generally all ORM follow this.

EDIT

Answer 1

I worked on an app with a 11 column primary key. It was always great fun retyping the list over and over and over every time I wanted to guarantee I was updating one row. It was a driver of bugs, MS-Access couldn't cope with more than 10 columns in a PK, etc.

Large composite keys are design smells that mean the table holds heterogenous entities or the designer wasn't really sure what it is that is unique about each entity. (Like assuming that hair color, eye color and body weight should be enough to unique identify an employee-- which isn't a good key because you'd need more and more and more columns to make it work and eventually that will include fields that are volatile and change a lot, like weight, or for some people hair color or lack there of.)