Because think about what Julian was trying to do.

He was trying to find a person genuinely good enough to be trusted with fourteen million dollars and a sacred family memory, a person who would use a fortune to do good rather than simply to enrich themselves.

And that is a nearly impossible thing to test for, in the ordinary way, because the moment a wealthy person announces that they are looking for a worthy heir, everyone around them becomes worthy, or performs worthiness, and the wealth itself corrupts the very evaluation it is meant to inform.

A rich man cannot find a truly generous heir by looking, because the looking changes what he sees; the fortune bends everyone toward the appearance of the goodness he seeks.