Answer:
Because if they don't have the qualities the person thinks they need then they won't be able to handle the memories in a logical and mature way. It's like choosing your successor, you wouldn't want them to be unprepared or to give them what you have and watch them ruin everything you've built to get destroyed because you made a mistake on choosing the person. They need to have specific qualities to fulfill the checklist and see if they're capable of enduring the duties that come with everything. They need to follow the same footsteps you did and continue the tradition.
Does this help?