Maybe some alien civilization does know about us, but it slightly afraid since we spec’ed in the war tree instead of space travel.
They kept letting us advance our war machines until one day they needed us. To help stop a greater evil; since they went space exploration instead of guns
Lots of scifi takes that route since we are very good at killing things. A well known version is the Asgard asking for help in Stargate SG-1 since they need more primitive tactics they’ve long ago forgotten.