Reading through some of their FAQ's they mention that some accounts have a monthly payout limit. Below is more information from their website on it:
A monthly payout limit is a restriction on the total amount of earnings you can receive at one time.
When you process transactions through Google Checkout, your payouts are sent to you according to the standard payout schedule. With a monthly payout limit, however, your earnings will be paid to you over a longer period. For example, say you have a monthly payout limit of $500. If your total sales in July equal $600, only $500 will be paid to you in July; the remaining $100 will be carried over to your August payouts.
Not all sellers have monthly payout limits. If you have a payout limit, the limit amount will appear on your Payout Summary page, Payout Summary Details page, and payment settings page. On these pages, you may also see a notification message asking if you'd like to remove your monthly payout limit. By clicking the link in the message, you can request that Google perform a simple review and remove your monthly payout limit so you can receive your payouts more quickly. (If you don't see these notification messages, you aren't currently eligible to have your monthly payout limit removed.)