Yeah I know it's not the usual outcome.

However one also has to consider that that stat refers to the main line of the family usually. Families tend to fracture over time. Either the heads of the family choose the main line or aristocratic laws did. Either way some descendants drift away over time from the main wealth pool.

But yeah, money tends to breed money. If it isn't managed by morons a sufficient amount will sustain itself, but failing enough business ventures can waste an unbelievable amount of funds.

For my family it's a mix of both, but primarily the last one.

In Europe it's not that uncommon to hear about old mansions, castles and estates in disrepair or for sale, because the old aristocratic families can't afford the upkeep anymore.

Often the lesser nobility ended up being nothing but farmers with oversized egos, and the spending habits of small kings. The industrial revolution left a lot of those behind in the dirt.