It's not just a killing off, but how it was done.
David was killed off in his second appearance in the same (film) series by a writer that co-created him. Rene and Robert were killed off after only one appearance by a co-writer that created the characters in the same (TNG/TNG film) series.
Icheb was a major re-occurring character in VGR. His death occurred "outside the lane" of VGR in a brutal, gruesome manor. Hugh was killed off because the writers were abandoning the Borg arc and didn't know what to do with him. Both spawned major backlashes the former examples did not. This can likely be explored in much further detail in episode to episode posts from 2020, Reddit, and YouTube commentary.
With the Borg revival from death process from "Mortal Coil" perhaps Hugh isn't really dead, and could make a surprise return in season 3!