Why is the protagonist called "The Lone Wanderer"?

[Das Boot]

One of the earliest side-quests in the game awards the player a permanent home, and it's very easy to get companions as well.

Thus "The Lone Wanderer" isn't alone and isn't really a wanderer either.

[Fake]

Because Ron Pearlman said so.

[Luis the Uma Loving Wizard]

Now that I think about it, that title doesn't make sense. The Vault Dweller make sense because that's what you were in Fallout 1, The Chosen One makes sense to because you were chosen to find a G.E.C.K. in Fallout 2, The Courier from Fallout NV has that title because of his/her former occupation and The Sole survivor from fallout 4 is exactly that. (if you're not including your kidnapped son that is). I guess the Lone Wanderer gets his/her title because he was kicked out of vault 101... I guess, Idk

[Eternie]

Well you wander around the capital wasteland most of the game .. how much time do you actually spend at your home? You probably have several homes and visit each of the main traders but most npcs probably still consider you a stranger or lone wanderer.
Besides that is how it's scripted in game.

[joje]

IMO the 101 dweller should be called "the scavenger" since thats what you do most of the time. Life in the Capital Wasteland is hard and there is no heroic characters there. The player character has never felt "heroic" in the dialogue. Feels more like a smartass kid scavenging and surviving in this hellhole.

And most of the quests are basically jobs for a scavenger. Retrieve random pieces from old buildings for the locals and doing odd jobs. You are expendable, they can send you between cities with a letter because your just a "scav".