For all our bulk IP APIs we have a extremely large number of IPs to return to you. We do this via API call with a default limit of 1000 IPs per API request. This limitation is by design as we want each execution to be simple and as fast as possible.
Each bulk API gives you an offset option to offset the IPs returned to you, you should offset by 1000 for each iteration of requests. When a JSON object is returned to you with less than 1000 IPs that will be the last available page for that specific risk level or threat type.