What does this even mean? People shouldn't talk about it because it doesn't have as many users?

Honestly the learning curve isn't that atrocious. I've always advocated for following a build guide then start looking at ways to personalize it at level ~70 (and with Exarch altars you can farm regrets to respec.)

Learning the skill tree is hard but it's made much easier when you have a base to modify.

The learning curve gets really bad when you start trying to craft though. And expensive.

Easily Path of Exile. There's something so relaxing about blowing up the entire screen with one flick of my wrist, and it really gets my endorphins flowing to minmax my stats using third party tools like Path of Building and testing out items on the trade site / changes to my skill tree to see how they'd affect my build.

To some people it sounds like work, but for me it hits that sweet spot of minmaxing and complexity that no other game really can.

Edit: I should also mention that lately I've been mostly playing on Steam Deck which has been a revelation for me. Endgame "alch and go" mapping is so perfect for the pick up and play style, only enhanced by having access to it from the couch/toilet.