That's my point. I have never known anybody to care about NPCs unless they were a DM or the NPCs in question were valuable henchmen. It is really impossible to create NPCs that are even half as detailed as PCs, because each PC has the player's personality behind it, whereas you have to play all the NPCs with just one personality; they turn out all the same or as cookie-cutter archetypes. Hitting that wall, that glass ceiling, was the hardest part for me. All the work I put into that aspect of the game wasted.
You still care about them because you've put as much as you have into them, but from a player's point of view they still don't matter. In my experience, D&D is an outlet for all the urges that remain ungratified in society, principly creativity and agency, but also frequently aggression and greed. And as I see it, it is much better to let those out in the game and be altruistic in the real world than the inverse.