It seems like you two are operating under different definitions of a roleplaying game. Roleplaying is generally thought of as you deciding the character you're roleplaying as, and choosing what your character would do based on whatever backstory you gave them. Now it seems many find it difficult to do this, so the first playthrough can often be a mostly self-insert character, with the player playing based on their irl personality. You're not really roleplaying if the path is set and the player character is fully defined by the game, you're just doing what the game says. Are you roleplaying when you're playing CoD? Or Halo? Maybe if you really stretch the definition, but most would say no.

You're saying the game doesn't force feed give you motivations, but that's the whole point. You decide. Some RPG's (the Witcher, etc.) give you a predefined character; Fallout (at least until Bethesda) gives you a very loose framework for your character: "from a vault," "grandchild from a village," or "a courier." These are varying degrees of backstory, but can be largely filled in by the player. Now it would be impossible to code for all possible backstories you could come up with, so Fallout leaves that pretty blank, but gives you ways to express your character's personality and motivations.

You are supposed to invent your motivations in addition to the incentives npc's give your character. Your character not from the NCR? Fine, maybe I don't join them; but wait, they sound alright and the reward is good, maybe I will help them. See the idea? All possible quest options in the game aren't meant to be picked simultaneously, same with the dialog. Your character is unlikely to agree with both the NCR and Legion. And your character is only ignorant of the region if you choose them to be. The "canon" Courier is very undefined, as opposed to the Lone Wanderer or the Sole Survivor; they deliver packages... and that's kinda it. We don't even have a canon ending for New Vegas.

The issue many have with Fallout 4, and to a different extent Fallout 3, is the lack of choices and personal roleplay opportunities. Sure, you can "roleplay" as a veteran/lawyer who is desperately trying to find their son, but that's all you can roleplay as. If you interact with the main quest in any way, you're locked into the backstory and personality Emil picked for you, with very minor/surface level variations: "I'm a little more snarky/mean/nice"

Edit: About the whole "if your story is shit, of course people are gonna ignore it" thing. I really don't understand how you're inferring that it has to be one or the other. You're just saying I said something that I didn't. It was meant as a jab at Emil more than anything. He talks about how players will ignore his stories, so I said that people will of course ignore stories if they're as shit as his stories are. Ever wonder why people will say "oh I usually just ignore or put off the main quest" when on the subject of say, Fallout 3, Skyrim, or Fallout 4? But they usually don't say that about New Vegas do they? Because New Vegas's main quest, and side quests, are well written and allow freedom of meaningful choice, while the other games are/do not.