From what I've seen of how FDev has released -- and not released -- updates for Elite Dangerous over the past five or six years, I think they take quite an unusual approach to developing new content for the massive, sprawling monstrosity that is ED. It may or may not be a necessity given the nature of the game, but in any case, I think this workflow makes big reveals less practical until closer to launch.
I think they work at a whole raft of stuff at once and they don't actually know 100% of what's gonna be going into the next update until quite close to release. I've seen people scoff at this, but I think past events support this being the case.
I think the code is spaghetti, I think the very concept of the game is convoluted for a small studio to work on, the breadth of the product means small changes in one area have unexpected knock-on effects on others. Seemingly simple additions can spiral in workload when they hit unexpected roadbumps the labyrinthine codebase, other additions go unexpectedly smoothly and can be ready before other features that are scheduled to come first.
I think this, combined with previous failures, has forced them into a just-in-time, flexible-goal, adaptable-approach type workflow.
See the failures during the Horizons season: promising a bunch of releases with specific features hitting specific deadlines, then running late on almost all the deadlines with many of the features appearing in compromised form... telltale signs of discovering too late they couldn't realise what was envisaged, after having promised it, putting them in the position of killing themselves to improvise the closest simulacrum of the original vision within the limitations of the software (e.g. multicrew). They clearly don't want to be in that position again.
You see it in Beyond with the last-minute delay on Ice Planets and Fleet Carriers... then Fleet Carriers reappearing in drastically altered form, and Ice Planet tech seemingly being iterated upon and rolled into Odyssey. (Also, a lot of the small details of the mining update being altered/dropped -- dangerous caustic asteroids, etc.)
You even see it in relation to the early rumours and leaks around Odyssey -- base building heavily indicated by well-supported leaks and even FDev's own HTML bean-spillage, lack of atmospheres suggested -- then we're surprised to be told base building isn't even on the roadmap but atmospheres of a sort are coming.
I'm almost certain they don't tell us anything simply because plans are changing constantly.
There will be as-yet-unannounced stuff currently planned for Odyssey that will ultimately go the same way as FCs and Ice Worlds did in Beyond.
I honestly think they feel they HAVE to keep quiet about 50-80% of the update because they don't fully know what's going to be in there, what will be suddenly delayed to the next update, what will be cancelled, and what left-field feature a skunkworks team (or whatever) will suddenly come forward with in almost completed form.