You're assuming you will be able to keep this capital forever. History demonstrates that most of even the richest families don't stay such after 3 or 4 generations.
Ask any Family Office managing finances for HNW investors and they'll give you examples.
* Decreasing marginal utility of wealth.
* Difficulty investing as wealth increases. Capital accumulation lowers rates, incentivizing individuals to spend (h/t Reisman)
* Empathy and philanthropy (one can't just ignore this, it's human action all the same).
* The calculation problem builds in inefficiencies as organizations grow (h/t Peter Klein).
Intergenerational differences in ability and goals and the squandering of inheritances.
Entrepreneurship and innovation. Punctuated equilibrium (h/t Schumpeter).