REST API List all VM's not returning all VM's

Through the Azure web portal, for a given subscription I see "x" number of VM's.  But when I run a query against the REST API, it only returns "x - y" number of VM's. 

Any thoughts on what the issue might be?

Invoke-RestMethod "https://management.azure.com/subscriptions/$($subId)/providers/Microsoft.Compute/virtualMachines?api-version=2017-12-01" -Headers $headers

As a side note, I have a much smaller subscription where the counts do match up between the web portal and the API using exactly the same call.