Treasure. As much as glory, or righteousness, or saving the world, characters (whether PC or OC, honestly, some of this applies to fiction as well) are motivated to go out and engage in adventuring or heroism by the promise of loot. Some of our favorite famous 'heroes' get involved in epic quests simply for monetary gain, at least initially. Conan, Fafrhd and the Grey Mouser, the list goes on. Bounty boards, quest givers, guilds, you name it, they motivate folks to do their dirty work by paying them.

But. In a lot of games, treasure doesn't mean anything. After a few levels, or the first few adventures if you're playing a game with a different means of advancement (like character points) it loses its luster. You have a lot of it, and nothing to spend it on. Or your game isn't even about getting treasure (which is perfectly fine) , but helping the less fortunate or just doing good.

But there the treasure is, still, in a lot of games. There are tons of it. Gold, gems, art objects, magic items. D&D 5e gives out a bunch of it, by default. Ridiculous amounts. It gets boring, and useless, pretty quickly. It destabilizes whole economies by throwing fistfuls of gold into places that used to be lucky to have copper or maybe silver. (That can actually be pretty useful for storytelling in some circumstances if you want to get into it.)

So, why even have it? Once the characters have a lot of it, why give more? One reasonable answer is: Don't. Stop giving out treasure once the characters have gotten what they need to live large. Let them earn just enough to maintain their chosen lifestyle, and motivate them with other things, like revenge or justice, or defense, or yes, saving the world. But that doesn't always feel satisfying either.

Another answer, and one I like, is give them more expenses. Make sure they have to build and maintain a stronghold, or a temple, or an orphanage. Make them responsible for whole communities. Tithe them. Tax them. Steal from them. (You think they were motivated by loot before? Now they want that loot back, and revenge on the thief...)

But. (I love that word.) There's a whole other layer to treasure that's getting missed, even with cool magic items. (Which, as others have said, need to be cooler than just +1 this or that.)

That layer? Worldbuilding. And in worldbuilding, specifically, lore and exposition. When the characters discover ancient coins from a bygone era, it's not just currency. It's an opportunity to tell them something about the world, about the time and place those coins came from. The metal used, the edges, the images on front and back. What famous ruler is depicted? What sigil is on the reverse? Why those, and what does that say about the culture that made them? Art objects are even more evocative. What do they look like? What do they depict? What are they made of? All those things tell you about the values of the culture they come from.

They also tell you about the people or creatures that had them. Were they art or currency in use by the culture of the person or monster you got them from? Were they stolen, scavenged, or looted from others? Why does that person, or that monster, value that kind of treasure specifically? Or is it just detritus left from their predations? That right there tells you what the creature doesn't value...but also what sort of being they fed on.

Where did you find the loot? How was it protected? Or not? Why? So much information there, with no long boring lore dumps.

Magic items are a whole other field for worldbuilders. What does it do? Why does it do that? A sword that glows blue in the presence of servants of a specific Dark Lord and burns them as it cuts says absolute volumes about a certain time, place, and culture, as does the construction of it, the material, the decoration (or lack thereof)!

A lance crafted to be especially deadly to dragons tells you those people had a real dragon problem...and warriors mighty enough, and well protected enough, to have a decent chance against one in a melee. Discovering it before you ever meet a dragon could tell you a huge amount about dragons in that world!

Honestly, the reasons just go on and on. What would Elric of Melnibone have been without Stormbringer? Without the One Ring, there is no Lord of the Rings. But on a smaller scale . . . the swords the hobbits got from the Barrow Downs are some of the finest examples of worldbuilding and storytelling in fantasy fiction. Introduced very near the beginning of the tale, they inform us about the conflict between the men of Arnor and the Witch-King of Angmar. They give the hobbits trusty blades to rely upon in many circumstances. And then, near the end of the tale, they shine, as no other blade would have been as harmful to the Witch-King, or even rendered him vulnerable to Eowyn's killing stroke. Sting, likewise, comes into the tale of The Hobbit early, and is significant throughout both that book and the Lord of the Rings, not only because of its power, but its history. Its significance to those who made it, and what they made it for.

To sum up, make your treasures epic by tying them into your world. Especially in the case of magic items, give them history and significance. Even a paltry +1 axe can be critical if you also note that it was made by the dwarves specifically to combat the Dragon Lord of Arragoth, and will be more effective against him (or even be his only weakness!) when finally brought to bear against him and his minions.

Go forth, and build a world, coin by coin, blade by blade! (Look, I used weapons in my examples, but gems and shields and armor and crystal balls and all that matter too: The Rings of Power,The Arkenstone, the Silmarils, Bilbo's mithril shirt, the Palantiri, the Aegis of Athena, the Armor of Achilles, Eilonwy's bauble, the Black Cauldron . . . I hope I've made my point.)

video here https://youtu.be/j2a0HAGW-5k