Speculative adventure games (aka TTRPGs) are just that: games. When all of the world design, history writing, and character building is finished there are only really five different places where your players really feel and pay attention to the world you have created: the places they explore, the spells (cast on them and by them), the monsters and villians they fight, the kinds of treasure they find, and magic items they use. These are the places where a DM puts the description of the world because these are the places where the players pay attention and the rubber meets the road.
How the places they explore are presented and if they are memorable or not has a big effect on what your players will remember. The way the traps work, hazards, weirdnesses, and the general feel of the place all say something about the world you have created. How often do places like this show up? How deep do they go? How weird do they get? Who built it? Is there any indicator as to who lived and/or worked here? This is how you get the history and feel of your campaign setting in to the minds of the players.
The way magic works also says alot about the world. Do spells have the names of their creators attached to them? Are there unique spells or ways of casting spells that show something about the world? If it is rare to find magic and hard to cast spells, then it colors the world in a certain way. There may not be any good wizards in your world. How the magic works would be a great place to accentuate that. Changing how the system works just a little bit can say a lot about spells and the people who cast them.
China Mieville's Slake Moth really brings home the setting of Perdido Street Station. Your monsters and villians are the probably the most defining element of the flavor of your setting. Are monsters (and demi humans) rare? Perhaps the only real monsters in your world are men with the occasional tentacled horror, or giant snake. The presence, size, intelligence and behavior of dragons says a lot. What the characters encounter really impacts the flavor of the world probably more than anything else because these are the things they fight and most of the interaction of most games is the combat system. When you fight a monster in a location the chances are someone is going to cast a spell. You can begin to see how the colors start to come together.
Treasure. It all comes down to what a large haul is. Do you find that dragons hoarde thousands of coins or just hundreds? In some worlds 300 gold pieces is small reward. In worlds with a little different flavor 30 gold crowns sets you for life. How far does gold go? How much do you find? Is the treasure even stacks of gold or is it historical artifacts and information about the world? What you find burried may not just be wealth but flavor.
Frequency and function of magic items works hand in hand with the spells and treasure. These things are generally a way for characters to touch the history of the game world. How they work says somthing about magic and the metaphysics of the campaign. Do magic items only ever show up based on fire and ice? Is it really just misunderstood technology? What magic items you present and how many of them you present is one of the best ways of conveying the world to the players.
These are the things your players will really ever pay attention to. These are the sticky points. They will meet you at these places and these are the things that they will remember. So if you want them to remember all the work you put into writing out histories and whatnot, do it in these places. Designing spells, creating magic items, building castles that will someday make a new ruin to explore, learning secrets about monsters, and seeking wealth are the ways players connect with the world. Fostering this connection by alowing the player to get involved allows them to remember more of what you have made.