And you think it isn't in ME3? You spend 95% of the game in the rest of the galaxy, saving small portions of it and witnessing firsthand how great the threat is all over even with much smaller Reapers forces than are congregated at Earth. Palaven burns, Thessia falls, a single Reaper controls the Geth and conquers Rannoch, the Rachni fall under Reaper control, and in the midst of it all there's Cerberus.
Just because the climax occurs at Earth doesn't mean the rest of the galaxy has ceased to be relevant. Quite the contrary,
the rest of the galaxy's troubles end up taking precedence.
Zevox