I feel like in the long run they are likely going to burn out.
I go through phases where I cannot read for enjoyment to save my life because my mind's all twisted up in knots.
So to untangle those knots I write, and that writing is fairly dynamic and fun to do.
Then my writing gets dull because I'm no longer in psychological distress from too many things going on, but from having expressed everything I wanted to express.
This is when I binge read, and experience my mind filling up, and relaxing, as if I'd not slept in a week and I was only now letting my head hit a pillow. During these times I cannot write.
The mind, for me, inhales and exhales. Pushing too much out of it leaves me in pain, but putting too much in it also causes pain.
At the same time, we experience stories all the time, whether it be through tv or friends. People who do not read are probably just inhaling different stories.
Remember that most of human history has relied on oral history. Writing/reading is not something necessary to the human mind, but rather an expedient of the same types of communication that the Bard or Elder would be using throughout and across time.
Someone does not have to always be reading in order to be a writer, nor do they always have to be writing, but I feel like everyone has a rhythm that they need to find out for themselves.