So basically, investors take a risk in the company so that it can expand and hire more people. They then get the benefit of a lower tax rate, since the government wants companies to expand and hire more people. More people employed means more regular income taxed.
It really is a win-win.
But they don't need that lower tax rate as an incentive. Incentives should be used to encourage one behaviour over another. Are those people magically going to earn that income as a salary instead?
The incentive to invest is that it allows you to grow your money. People will do that even if the tax rate is HIGHER than salary earnings, since they want to grow their money, and they can't do that without investing it.