While I agree that the two tags are similar, I don't think that they can simply be merged. I see more of a case for removing lore outright, but I'm reluctant to do that blindly.
The issue is a simple one: How do we handle a question about a game-world that isn't related to the plot? Asking Why are there are no tanks in Fallout? isn't an important plot point in the game -- it never comes up -- but that doesn't mean it's not an interesting question.
Some games have the benefit of having an established game universe, in which case a better choice might be game-series rather than game and lore, as evidenced by the portal-series and half-life-series tags. (There's even a fallout-series that the New Vegas question might benefit from)
I think the best course of action may be to simply remove the lore tag entirely. Though it doesn't have a tag wiki, I would define Lore to be any question focusing on the plot and background of a specific game, or a suite of games. In the case where there is only a single relevant game under discussion (such as this Terraria question), it is okay to use only the game tag. Popular franchises, on the other hand, would benefit from a game-series tag instead, as they may be relevant to more than a single game.