Here's one reason.
While it is admirable that the Haitians fought for their freedom, their country is a mess. The reason their country is a mess is because they never established a stock market in the 200 years that they've been free. A stock market is something like the New York Stock Exchange, or in Japan they have the Tokyo Stock Exchange (TSE), or in the UK they have the London Stock Exchange.
A stock exchange is an easy way for international, institutional investors to exchange money, or to invest in another nation's economy.
For example, if you live in Australia and you think the American economy is doing really well you can invest in the Dow Jones Industrial 30, or the S&P 500. Those index funds mirror the best American corporations. Every nation has an index, which is basically a list of the top companies in that nation. The Dow Jones average is the top 30 American corporations, the S&P 500 is a composite of the top 500 American corporations. An Australian or Brazilian investor doesn't have to do any research if they want to invest in America. All they have to do is buy shares of one of our index funds.
Haiti doesn't have a stock market and thus there's no way to invest in their economy.
Think about it, if you could invest in the best manufacturing companies in Haiti you could invest, say, $5 million, and they could use that money to buy supplies and build their business. Or you could invest in a Haitian tech company, or a Haitian retail chain. In the absence of a stock market those investments are impossible.
So to answer the thread starter's question. The Haitian revolution was over 200 years ago but they haven't finished. They haven't established a stock market so people can't invest in their country.
I guess the paradox is that since you can't invest in Haiti's economy they have no debt whereas in America we sell government bonds to anybody that will buy them. As a result our National Debt is over $27 Trillion at the date of this writing
So we're $27 Trillion in debt and Haiti has no debt because they don't sell government bonds. So in one way, Haiti has more money than we do when you factor in the National debt.