For me, its the ability to win a 1v4 even if its a small chance. If youre the last man, you still feel like you have a chance. This is why halo struggles with one life modes.
For example, gears of war 1’s execution one llfe mode was its most popular mode, then in gears 2 no one cared for it anymore because 1 v 4’s where impossible. gears 2 also went to 5 v 5 which made it harder to come back. who wants to play a one life mode when they know theyve lost when a couple teammates die? thats why battle royales have respawn stations so you still feel like you can win.
gears 1 worked because instant kill shots required skill. sure aiming became easier the closer you got but it wasnt much due to how the shotgun spread was (unrealistically) designed. this meant movement and aim skill purely complicated each others high skill ceilings. it was ok if you missed too because you still do some damage. This type of weapon helps creates interesting fights and it helps all skill levels have fun together while also promoting a high skill ceiling.