The best reasons for doing nothing.

Being dead.
Being Asleep.
Being Switzerland in a military conflict. (Because they do lots more than nothing in everything else.)
Having a snow day.
Being Paralyzed.
Being given a beating. (But seriously, who does nothing when that happens?)
Being a big fat politician in someplace.
Like Washington.
In all of these things, the people who aren't performing action technically can't help it. It is in their nature.
Now, obviously sometimes, people who have to capability to perform an action choose not too. Like a couch potato. Or someone who is clinically depressed. The couch potato chooses not to move because they are lazy. The depressed person does not move or act because they figure, why bother? In this sense, philosophers are clinically depressed. Or lazy. Or both. But they do think an awful lot. So I suppose that counts for something.