Benjamin Olson
Hero
It didn't exist before the 90s though, and "Murder Hobo" goes back to the 80s, if not the late 70s.
Well, technically it did exist before the 90s, but that history is really neither here nor there as nobody is searching pre-90s internet.
While predating the internet would explain the origins not being revealed by internet research, it wouldn't explain how the term would not be attested in internet usage for many years of the internet being in wide use, with tabletop gamers not being particular rare on it.
Are you asserting that variations on the term were in common use, or that the precise term "murder hobo" was in common use going back to the 80s? Once again I think it is perfectly believable that variations on the term were in use, but the specific phrasing is grammatically improbable to have won out without some form of mass communications at it's back, which would leave us with primary source attestations.