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 work and effort. D&D seems to have evolved from a game of random tables and strategy that required constant improvisation from the DM, to a game of (open ended) story telling. Character death seems to be less of an option.
So now DMs think they need to build a complex story, while allowing players to make choices. They need to prepare challenging encounters that aren't too challenging. And D&D combat tends to repetition, so they need to find ways to spice it up.
The handful of WotC modules that I've seen don't support that. The module has a single path and a bunch of dull combat encounters.
This. I'm reading the Cyberpunk RED sourcebook now. I really appreciate the GM hints and suggestions. I don't remember anything like that in the 5e DMG.
Worse, some rules/features are holdovers from previous versions that don't make sense in the current game.