If you want everything to be level 1 when you go to a new area, or for the game to become completely unchallenging after you hit level 5. That is what you are asking for.
This is hardly what the people were asking for. Its more that they a lot of people have experienced severe autoleveling with past Bethesda games, and believe that it can take away from an experiense.
Nobody here wants to have only level 1 mobs appearing throughout the game. But a lot of people would feel cheated if, at some point in level progression, all molerats were to be replaced with Tunnelers, DUST-style.
I'd guess that people expect a healthy mix of different leveled enemies and creatures where they make sense.
No that is exactly what is being asked for, the wasteland is setup with no level locking and it starts out with bloatflies and molerats and ends up with albino radscorpions and deathclaws. There are encounter zones that are set to stop at the level the player enters them, most of the downtown areas. However they are also leveled to spawn enemies around the players level with modifiers for normal, hard and boss enemies. Most of the areas are structured this way and so is most of New Vegas. Some areas in both wastelands are setup with static levels of creatures like The Deathclaw Sanctuary or Gypsum Trainyard. To say that New Vegas is setup differently than Fallout 3 in this regard is complete and utter nonsense. They both make use of the leveled spawns and encounter zone systems. The DLC's are setup in almost the exact same way in both games. New Vegas makes less use of the encounter zones in the wasteland (which are setup by region) but it still makes use of them in many areas.
This contributes to how boring and unchallenging New Vegas's wasteland is especially when you arrive at Doc Mitchell's at or above level 30, and that would be the point of such an optional. When you arrive at New Vegas after completing most or all of Fallout 3 you are level 50 and maxxed out, especially with all the OP mods people use that uncap level and give them perk per level and other ridiculously unbalanced things. Why even play the game if you just walk around one shotting everything, no, we're not going to cater to that play style at all. I don't find that fun, and I don't find ridiculously unbalanced and boring mods like Dust fun either.
I need a snickers...