Not only does it take time away from writing, but it also it is an antithetical activity to writing. These aren't actors, whose craft involves a projection of self and whose careers consist of creating a positive image in the minds of their audience. They work alone. They hide from the sun. They don't always play well with others.
Some writers refuse to go for a spin on the publicity machine.
Everyone else is expected to suck it up and be friendly and smart. For most writers, that isn't too tough. Still, some writers just can't do it. They use a pseudonym. They don't want to give away details of their personal lives, knowing that once those things become public, they can never be taken back.