some investors may only want to buy in if they can get a controlling stake in the company. I think this is why the founders may have to sell some shares. For example:
300 mil shares available for sale
plus extra 10% from agm another 180 mil
plus 200 mil from founders
= 680mil
makes a large investor the largest shareholder. Which if I was going to fork out $100 mil you would want to be.
(obviously these numbers are loose guesses)