A family I grew up with has a net worth of ~$20B but it's layered through hundreds of LLC's. Easy to understand the truest wealth figures avoid publicity the most.
Two other families nearby hit the ~$2B range but you'll never hear about it unless you're floating on a boat when their name comes up.
Bulk of the worlds wealth is held by unknown(or at least non-famous) people. Anonymity and low key profile helps them escape being in spotlight. Being invisible to tax agencies, crime rings and mobs among masses is far more preferable than having a celebrity profile and a photo on forbes.
Also its easy to bequeath your descendants wealth easily that way.
Two other families nearby hit the ~$2B range but you'll never hear about it unless you're floating on a boat when their name comes up.