3D Hubs is expelling hubs that cannot meet their minimum requirements. For instance, if a Hub has not signed up for Instant Order, where the customer can upload and pay for the print in one transaction and without Hub review, the Hub is no longer allowed to use 3D Hubs. Another requirement is a minimum customer approval rating and a minimum on the number of orders that get cancelled for any reason, even if that reason is to comply with 3D Hubs rules such as no weapons.
3D Hubs is also implementing a minimum order amount, though any customer who is willing to make the minimum order is welcome to place an order. It is only the Hubs that are being booted.