B4: The Lost City is a classic module for D&D. At one point it (in)famously stops giving full description of the rooms but instead lists monsters in each area and tells the DM to figure out why they're here themselves. Once the reprint will show up in new anthology, I'm sure people who complain online whenever WotC uses "ruling not rules" or "DM decides" or "these parts were left for the DM to fill in" in their design (and then continues buying WotC books to keep bitching and doesn't touch 3rd party or other games for some reason) is going to be normal about it. /s
It's not the anger that's cowardly, it's the refusal to try. It's taking any other path, so long as you don't have to risk your own stupid pride. Have the humility to accept you might not make the right call, but the courage to actually make it for yourself.
This adventure comes from a time when modules were a toolbox. One of the most popular modules from the era had a plot of "there's a bunch of monsters in some nearby caves, and they don't all like each other". Tunnels were blocked by debris, allowing the DM to connect it to another dungeon they wanna try. You might come back to the same dungeon a second time, and the contents of the room will change. A module is a starting point, but the DM continues the story from there.
If you don't know how to prep that, then the empty room is a boon. If you do, then the empty room isn't an issue. If you don't want to prep a campaign like that, then maybe this style of module isn't for you in the first place.
"It's not what they're doing that's cowardly, it's that they're not doing what I want them to". Your argument is based entirely on the fact that you are demanding that they be more creative. The assumption that they have nothing else to do and no other motivations. What right do you have to tell other DMs how to run their stories? You can add all the filler you want to your campaign, but you're demanding that other GMs have to deal with your filler too, and accusing them of cowardice when they perfectly reasonably tell you to sit and swivel.
Ok, let me stop you there. We do not live in the 80's. We are not restricted to Gary and his friend's single system that has been invented. We are not fumbling our way through discovering how TTRPGs work, experimenting with vague outlines to see what happens. It's been 40 years, we have better everything now. Our superdungeons aren't just a series of deathtraps and random encounters to kill the players. Our modules aren't just a list of encounters held together by the vague pretense of a story. Our systems are able to handle nonhuman ancestries. They're not releasing the adventure for Dungeons and Dragons Basic Set. You can call it a style, but it's a "style" born of experimentally bumbling through unknown territory - if anything, by choosing to stick to it in an age where we've massively advanced the mechanical and storytelling techniques of TTRPGs instead of learning to run more advanced stories could be classified as cowardice - too cowardly to learn what's changed, too cowardly to risk more advanced narrative, too cowardly to try new things. Hey, look, when I create an unfair dichotomy you're the one that gets called a coward. Weird.
What do you think is relevent about this? Are you not able to add things to your campaigns without those hooks, or do you believe they've disappeared from modern adventures? They have not. like half the tunnels in my current campaign are described as "beyond the scope of this adventure". Honestly, it's kinda worrying that you apparently need these structures in place for you to be inventive. If you want to argue for the creation of a learning series that would help you with things like this, go ahead, but once again, they are selling this as an adventure, and should be providing a complete adventure.
Why? What are you even prepping? What is there to prep in the room? Like you said, it's just an encounter and a featureless box. Put a desk in the room to, uh... "to make the fight a little bit more interesting" [sic]. What's stopping you from inserting your own empty room to add an "interesting" table to? Why do you need WotC to push this prep on GMs looking for a preprepared adventure?
I ran quite few old modules and I think it's doing them disservice to just assume their design philosophy was inherently wrong or flawed. Yes, we developed many different ideas and perspectives over the years but they were often aiming for different things and old modules are, I notice, often very good with presenting PCs with a situation and letting them go wild with solutions. I think I prefer them to modern WotC or Paizo formula of a strict linear plot
I do not believe you have run a modern module if you don't think they let players go wild with solutions. They might include a solution instead of leaving it as an exercise for the DM, but they very much let players approach them however they want.
Anyway, putting random monsters in a room and telling the DM to figure something out is inherently flawed. It's literally incomplete, and has filler encounters. Those are definitely flaws in a prepared adventure. As I've repeatedly said, they wouldn't be flaws in a different type of publication, but we're not discussing that type of publication.
Also, you forgot to defend your actual point. Even if they weren't flaws, how would that make people who don't like that "style" cowards?
I have run Lost mine of Phandelver, several of Dragon of the Icespire Peak adventures, two and half modules from Candlekeep Mysteries, one from Twelve Peculiar Towers, one dms guild adventure, I think this is far from not having run a modern module as you accuse me of.