Mrstarker: Underworld may have come out before Wolf 3D, but surely there must be people out there who still remember System Shock or Thief which are in many ways part of the same lineage, same design philosophy.
Thief is a living series and System Shock had an enormously popular sequel many years later. Underworld's recognizability pales in comparison. The Ultima brand might still carry some weight, but the Kickstarter isn't for an Ultima game.
Underworld is hardly an obscure series. It's just relatively less exposed than the biggest-name games. I haven't been following this project, so I don't know how successful they were at raising awareness before starting their drive. 11,000 backers and $620,000 isn't bad at all. Enough other people remembered the lineage to fund the game, even if it wasn't a day one success.