can someone explain the rage engine to me and how every death animation looks different every time?

i don't know much about game development. but i keep hearing about gta 6 is getting rage 9 and rdr2 was rage 8. could someone explain what the rage engine does in rdr2? also how is it that every ragdoll animation is so unique every time. I've tried to look into it but i haven't found anything i really understand yet. I'm just curious about all the tech that goes into these games.