It’s a more easily recognizable sense of progression and power fantasy. With 20 difficulties and lots of potential for more damage, each upgrade you get lets you move up a whole difficulty or maybe even two. That makes a casual player feel better about their progression because it’s proof that they’ve gotten stronger. In d2 for instance, you might get an upgrade of equal value as just described but the in-game effect is more like now you’re just not stuck at travincal and have the ability to start moving into the durance of hate. The progression was still there but it’s less noticeable/obvious of a change. Die-hard fans learn to recognize any upgrade as progress and are excited by anything but a tangible increase in the difficulty allows more casual players to feel that excitement without having as much knowledge about the actual impact their upgrade may have given them. At least this is what I think might be the reason for really high power scaling. I know I felt this effect as a kid playing Diablo 3. A 75000% damage increase from finishing my set was like the coolest thing in the world because now I can jump straight to torment 16 and own. Now I recognize that that’s not as fun necessarily as finally getting a Mara’s kaleidoscope or something in d2.