The harpoon was a sort of skyhook, wasn’t it? I don’t know why they didn’t have a thruster. It wouldn’t have required much - just some compressed gas, maybe. Tried and true.
The had a nitrogen thruster to push the lander against the comet so the landing pad "ice screws" could "drill in" to hold the lander down, after the "harpoon" dug its way into the "icy surface of the comet." That all failed. Oops. The thruster failed to operate. The lander did not stay on the surface so the leg screws could attach, instead the lander "bounced" one kilometer into space before coming down and "landing" without another bounce (how was that accomplished? Or was it really a "non-destructive crash landing?"), apparently, they say on its side, in the shade of a cliff where it will only get a portion of the sunlight it needs to keep the battery charged, a kilometer away from the carefully selected landing site, with no way to try again.