Personally, my experience has been that a philosopher's use of language has a non-trivial relationship to their thought. This isn't to say, like, some kind of indecipherable, private language is going on but, rather, to some degree, pushing forward in new and different ways of thinking in philosophy entails pushing beyond the norms of ordinary language. Learning more about the philosophy also clarifies why the novel uses of language are useful in articulating it in ways which avoid pitfalls, cliches, etc.

So I think it can be reasonable that a philosopher would respond that a critic does not understand. If a philosopher was entirely incoherent, not just difficult to penetrate but impossible, then no one would give them any attention. There has to be a glimmer of something there for one to put in the effort. In contrast, by the same coin, it's not hard to come to the realization that, beyond the jargon and complex syntax, a text is truly unremarkable or pantomiming nonsense.