My guess (lemme see your brains!) is that you’ve never been in the mood to unpack all the systems you need to really get rolling, at least for GD. Unless it’s just a flavor thing; I dislike the GD flavor but the game’s good enough to make up for it.
There is a large cognitive burden to understanding how items, affixes, mods, skills, and constellations work in GD that is orders of magnitude above D2. D2 is extremely straightforward by modern ARPG terms; it’s just not that hard to figure out “big numbers, hit harder, more loot!” You basically don’t have damage channels to worry about, resistances are real damn obvious, skills are kinda right there.
I don’t mean this as a bad thing! I love D2 too, and I’m surprised at how much fun I’m having with D2R.
I just mean that I could see someone bouncing off the newer games in favor of D2R because the system is easy and comfortable, the same way I can sort of float along in the d20-ness of the Pathfinder games because I spent so much time in d20 land that the system is easy and comfortable for me in a way that the 5E in Solasta or whatever requires a lot more thought.
All that said! GD is the best ARPG ever made, and I highly recommend it to everyone in this thread.