Modules that are "easy-to-run" for me often just merely look like a space to have a fight or the most basic of interaction. "When the party begins a long rest, five goblins will come out to attack them. DC 15 Perception to notice them if a PC is on watch. If captured, a goblin will reveal the hobgoblin leader in the cave across the way has three people being held." To me... this is like barely an encounter-- where you could replace the entire fight with the party finding a piece of paper on the ground that served the exact same purpose. So why bother having it? Oftentimes most of the 4E modules from the online Dungeon were like that... a series of three fights that had the barest linkage between them to inspire the PCs to enter this three-encounter gauntlet and fight their way through. I mean I can come up with three fights on my own and pay the barest lip service as to why the party is going to fight through them, I don't need someone to print that on paper for me. But if the adventure tells me why these three fights are a part of a larger ecosystem of the events going on in the area, and various bits and bobs of information and objects the party could discover from them that will breadcrumb them to other locations that are driving the narratives of the various enemy NPCs... I am getting a larger world within which to improvise around.
I think you're maybe not familiar with the newer (by like a general "length of TTRPGs existing" newer) modules that I think many of us are point at when we say "Easy to Run." I'm going to use the excellent Winter's Daughter by Gavin Norman as an example (released 5 or 6 years ago?). It opens with a set of Referee's Background that tells you the story of the situation at hand (an ancient fairy prince, the war between him and mortals, forbidden love between his daughter & a mortal knight, etc). It gives some stuff lingering about how the princess and the knight's shade are stuck, various context for things within the tomb and beyond, etc.
You get a set of hooks. A bunch of Common Folklore to present the players as their background or as they desire to investigate the tales behind the tomb before making an expedition. So on.
But once you're at the tomb (or at least the forest leading up to it), you have simple clear keyed maps with super usable and concise descriptions using the
BOLD (amplification) house style:
"
Stairs into the Mound
Descend 20’ (into the earth).
Dusty
(caked with centuries of undisturbed dust).
Deathly silence (disturbed by
PCs’ footsteps).
Dank smell (moist and mouldy).
▶ If examined: Scratches are discovered. Looks like something heavy was dragged up the stairs (a long time ago)."
You get random encounters that are more then "Skeletons: 6" and of course you have classic reaction rolls to make if the encounter doesnt have a custom one (
Reaction: Welcome strangers to join the dance. Attack vehemently if any of the coffers are disturbed.)
You get Referee's Notes with little extra bits right in the keyed room where they apply.
Everything is organized so you can look and speak at the table without needing to "prep." NPCs have Wants and Knows. They may have some boxes of Pleas or similar. The keyed maps have even more concise descriptions of the rooms along with their names so you can run just off it and look to notes as needed (eg: 11. Statues with weapons: Mould-patched walls. Partially concealed mural.)
When I read this module for the first time about 3 years ago, it broke my mind. I was in the middle of running Curse of Strahd and a stitched together Eberron campaign, off of pages of long form text I had to extract useful stuff out of, and often never gave me the important to play items at all. I discovered you didn't need all that, you can fold narrative things at the start of a chapter or module and then focus down on moment to moment play in a well keyed and written map. And doing this actually gave me more space to respond to player ideation in a rigorous and smooth way.