The short answer:
Lack of technological advancement.

The long answer:
Every period of history had men in power. Some few where better than most in a way crucial for history period they where born (physically stronger, healthier, more intelligent, born in better family and environment etc). They held most of the capital. So far, that has not changed till the present day. It is the same, more or less, for any type of government and economic system. For example, in ancient Egypt, pharaoh held 500 coins, while common people held 1 coin. Today, "pharaoh" holds 30000 coins, common people hold 3 coins. I used the term coin as any form of power, not just the money.
The only thing that rely helps us is science and technology. With them we live way better than some wealthiest people from older ages. Technology makes your 3 coins bigger than ancient 500.

Conclusion:
You should thank science and technology for your well-being and allowing you to live the way you live today.