The point is that is the price the private investors who will be liquidating, including the company itself, are accepting for their shares.

If they are too far below the perceived value, they are leaving significant money on the table.

If they are too high, the institutions who participate in IPOs will let them know. If the price craters off IPO it is not good for perception of the stock, and so ongoing health of the company even if that maximizes private investor value at IPO.

So they build a book of commitment around the target value, trying to leave enough incentive (15-20%, often) of an initial bump to get big money in.