For Kafka--I think his writing is deceptively simple. There's no verbal clutter. And I think we all recognize ourselves in the absurd situations. I can't deconstruct him either--that's as far as I get.
To be honest, Nietzsche is not one of my preferred authors. I once had a philosophy professor who advised me that Nietzsche's philosophy was "powerful". Just can't get there. Same thing with Herman Hesse--very popular, especially among Nietzsche enthusiasts, but not for me.
Reading is such a personal thing. We form relationships with the authors, and it's kind of like friends. Sometimes they click and sometimes they don't.
As for effortless--every now and then (less so than in the past) writing flows for me and I don't know why. I guess talented authors can tap that well more regularly. It's a kind of magic and wonderful when it happens