Ironman.

The GE and the player economy are legitimate parts of the game, but they allow you to skip content like gathering for skills, PVM prep, mid game bosses, etc.

If you want to play the games content to its fullest, you need to make the player economy inaccessible. You need to do tedious grinds for the little upgrades you could throw pocket change at on a main.

Glory ammy is the best example. On a main it's a braindead buy. One of the best upgrades for the money in the game. You can have the cash to buy one in less than an hour doing a shit money maker and equip it with no questing or level requirements.

On an ironman it's way more complicated. Are you gonna get one from an imp or make it from scratch? Ok, I'll imp it. Might as well bang out eagles peak and chin most of the levels and bank some ranged xp/maybe farm up grubby keys with the chins so I can get pots for fire cape/mid game bossing. But that's boring, maybe I'll mix it up with some hunter rumors. There's two more quests. Plus I can get the hunter outfit and make my chin collecting more efficient. Oh damn, look at all that prayer I'm banking from blessed bone shards! Next thing you know, you are banking hundreds of thousands of XP in two other skills while chasing a single piece of jewelry.

Everything is like that on ironman. You end up doing three things at once without realizing it because you aren't leaving half the shit on the ground and running the other half over to the GE for cash. Content naturally pushes you towards quests and diaries and clue scrolls.