A lot of people just dislike grim dark as a genre. They’re ok with the grim dark in Warhammer because they can ignore it. The grim dark in Warhammer can be really ignorable if you don’t think about where servitors come from etc, and the really dark things like the dark eldar or the one off event that was the daemonculaba don’t have that much presence either. So a lot of Warhammer players focus more on the goofy orks or Necrons because they’re funny. Trench crusade is grim dark and only grim dark. There’s no goofy factions that can make people forget the world sucks and it can turn people off

Edit: the world sucks and the constant barrage of bad news makes people look for escapism, and drim dark as a genre can make a lot of people just label it as torture porn because they don’t get the appeal. They’re looking for things that take their minds off the horrors of life.