Earlier quoted context omitted.
To give liquidity to investors.
The cost of that liquidity is missing out on realizing future growth though. It's fairly safe to assume that as there isn't an IPO yet the investors want to hold rather than cash in returns. They probably believe there's more growth potential, and that the board are the right people to deliver it.
Why would it be? I don't believe an IPO has to be dilutive, it can be done with already issued shares. I grant you that's not usually how they're done though.