I happened upon a comment that he made on social media a few months ago where he explained his absence. In summary, he hasn't felt the spark to write for the public for a long time. He continues to write for himself, but he has not felt the inner compulsion that he deems necessary to do that work for the eyes of others.
Every writer has been there in some form. I've come up with some ways to battle writer's block when it happens. But they don't always solve the problem, or at least at the rate I'd like them to.
At other times, you just have to do something besides writing to get the juices going. Sometimes some other creative output like music or doodling can help stimulate your writing.
There's also something to be said for waiting until you're really ready to write what you want to write about. You may need to do the research that you need before tackling a topic you don't know as much about (and those you do know more about, too).
If what you want to write about is of a more personal nature--a story from your own life that you believe may benefit others, for instance--you may need more time to properly capture what happened. A few years ago, I saw Diana Butler Bass offer the advice that you need more time and distance when things aren't so fresh and tender to have proper perspective on an experience that you want to share with others.
It took me over seven years before I could finally write about a painful time that taught me about self-care and boundaries. I thought about writing about it sooner many times, but every time that I tried, I couldn't do it. I didn't want to relive it, let alone share what was to me an embarrassing episode with others.
A famous writer is in hot water about this very thing right now, having announced a life transition that would knock many to the floor for an extended period of time, and then a few months later announcing the impending publication of a new book that will tell everyone all about it. You shouldn't skip crucial internal work in the name of creative output.
All of this is to say that if you're a writer and you're feeling stuck, there are things that shouldn't be forced before their time. There are ways to tinker and get the spark back, but there are also dangers in trying to make something come about before it's ready.
It's better to go the long way around to find a genuine inner compulsion than to take shortcuts.