Limiting the number of items returned in an API is normal, and common, as otherwise you could end up making a call that takes a long time to process, and returns a huge amount of data. The most you can return in this instance is 1,000 devices, and then you have to make a second call, with appropriate pagination details, to get the next 1,000 and so on.
More detail on how pagination works within the API can be found here https://developer.cisco.com/meraki/api-v1/#!pagination/how-does-pagination-work-in-the-dashboard-api