In technical fields, we usually expect people to immersive themselves in a particular vocabulary to be able to understand difficult technical books, yet in philosophy we often expect these texts to be readily accessible to laypeople. Why? Derrida's work emerged from a tradition heavily influenced by Heidegger, Husserl, Hegel, Freud, Nietzsche and others, all difficult authors in their own right. Of course we might find it disappointing that these texts are not accessible to the general public in a way that, say, Russell's popular writings were, but isn't that nevertheless an absolutely valid choice on the part of the author?
Also, it should be pointed out that the so called postmodernists were not the first to employ a very difficult writing style that we might on first glance perceive as obscurantist: Heidegger is a good example of someone who coined a ton of neologisms because he thought it necessary to escape the traditional discourse. You might not buy his argument (I'm not sure I do), but Heidegger felt he had a good reason to distance himself from the existing discourse.
Are the main texts of postmodernism dense and hard to understand? Sure. Should they be a required reading for everyone? Of course not. But I don't think they are necessarily negative and I don't agree that they have no 'recommendation for what anybody should actually do'. Even Derrida, arguably the most deconstructive and 'negative' of the bunch, can be applied in a myriad of 'positive' ways, this is doubly true for authors like Deleuze & Guattari, for example. I think it ultimately depends on whether you view a critique of political or social structures as purely negative. I would argue that such a critique offers an avenue for change, by enabling us to see the status quo as something that can be attacked, rethought and then reformed.
But those are just my 2 cents on why I like (some of) the postmodernist authors. I think it's absolutely fine if not everyone buys into their thinking, I would just wish for a more honest engagement before dismissing them out of hand.