I think the key is that some people like ASI to the degree that it incentivizes certain race/class combinations that feel like classic archetypes, either in reference to fantasy literature or just to dnd itself. In my experience, players, often guided by the dm (myself included) will end up following these incentives, thus creating elven archers, tiefling warlocks, halfling rogues, gnome wizards, and so on. This being the case, when a player decides to do something non-"optimized" (again the statistical difference is slight) it feels different because it's not so common. (and I guess some people interpret player options to be valid for the entire race in the implied setting, but that still baffles me).
This approach has a couple shortcomings. One, it's a quite roundabout way of reinforcing archetype. I can see the appeal of archetype, but if you want that game...just play OSE. Or 5 Torches Deep. Or, pick up the free basic rules for 5e and just play with those. The options included just in the PHB can easily produce race/class combinations that veer away from classic archetypes, and that's before even getting to the inevitable options bloat for any edition.* Two, people want 5e to be a more open-ended game. They want to look at a character from a comic, or videogame, or movie, and try to recreate that character using 5e rules. It's not even playing against type, because it's just a different set of archetypes/figures all together. And race ASI just gets in the way of that. Of course anything is possible, you can play a slightly unoptimized character etc etc, but I think for a lot of people it's a legacy of the game that hasn't really been relevant for a while.
*case in point
Is a Tiefling Paladin against type? Because in 5e, Paladin synergies with Tiefling charisma bonus.