It's thematic reading and trying to shove stuff into genres in order to frame them rather than just enjoying the damn text. I teach writing and reading and it just made me cringe to read that tweet.
Kafka is excellent in particular because it needs no real analysis beyond the fact that it's pointless and bleak. It's throughoutly negative in point, highly absurd, and kind of scary. Now, there are plenty of things that can be analyzed out of them. But the surface level bleak nonsense of Kafka's worlds is just incessantly compelling.
I think that what you focus on is that Kafka's work was supposedly as bleak or futile as could be. But, of course, this isn't true; plenty of other writers who are bleaker, regardless of what the focal point of bleakness would be. Same goes for futility; in many stories by Kafka the futility is relative: you won't achieve what you wanted, but at least you can continue to exist doing a subset of what you like (examples include the novel The Castle*, as well as stories like The Burrow, Arabs and Jackals etc).
For me, when I was a student, the allure (the conscious allure, anyway) was that the worlds in the stories were dark but refined, with usually some kind of game of trying to establish whether if you can rise in that world is even possible. Perhaps that is why the protagonist in The Castle claims that his real profession is a space-surveyor.
I don't agree that you shouldn't care about biographical stuff, let alone when you have the author's own largish diary
Kafka has a host of quotes in biographical material which echo the hypochondriac element. A good example: "You shouldn't cheat on evil** by not allowing it its fair share".
*Of course in the end of the Castle (which wasn't written), the protagonist would get official approval to keep living in the village, along with official dismissal of his request to enter the Castle, and (more importantly) he would get that message in his death-bed in the village.
**likely he meant on stuff which are directly against you, like his self-reproaches.