Shares aren't just handed out for free, you have to apply and...

Shares aren't just handed out for free, you have to apply and send funds for the shares you want to subscribe to and not everyone does.
Typically there's an application limit of $15k per holder.

The total of funds received are tallied and if the SPP is oversubscribed then whatever you applied for is scaled back proportionally, e.g. if applications received are $4m to raise $2m, everyone gets 50% of shares they applied for and the difference is reimbursed.