One day all of us are going to die. The data we have in our social media accounts will linger on if we don't set it to be purged upon our death.
Once we are dead our data will slowly become toxic over a period of time. In the meantime, it would remain relevant for a period of time and social media sites like facebook will be able to monetize it by selling data to advertisers and the advertisers will unwittingly be paying facebook to sell to the dead persons.
It makes sense to adjust the settings now itself or get someone trusted to do it upon our death.