In my opinion, it is to create a supposed tragic ending of a person to a beginning of second life full of choices in another world. The ending is just a beginning is what I always hear nowadays, so maybe this is the reason. To create an idea that we can start with a new life and new adventures after death and maybe because there is a great chance that no one will survive being hit by a truck that they will be dead on the spot. no turning back. unlike other stories that will end by making the character alive after an accident or being in coma while having an adventure somewhere, in Isekai, the stories will just go on and on as the adventure will never end. I don't know if this make sense 😄. haha