Sounds like pulling the pin just arms it and the impact does the rest.
Safety considerations. Perhaps the grenade is not fully armed until the parachute deploys or the grenade impact fuse requires a certain amount of force to detonate. You don't want a super sensitive fuse active before the target is selected.
The grenades are good for overhead attack because the armor is not thick on top. Throw one of these at a tank from the ground and you may hit thick armor. 200 mm of armor penetration is generally not enough for, say, frontal slopes or a turret front. But drop it straight down and you go through 40 mm of armor like a knife through butter. Use a second one to penetrate if the first got defeated by the reactive armor panels.