Why is the Fulfillment REST API limited to 1 tracking number per fulfillment?

[JonathonMinard]

The Fulfillment REST API documentation states:

"With the REST API, you can set only one tracking number and one tracking URL per fulfillment. If you send multiple shipments with one fulfillment, you may want to specify tracking numbers and tracking URLs for all of them. You can do it with the equivalent GraphQL FulfillmentCreateV2 and fulfillmentTrackingInfoUpdateV2 mutations."

Why is it that the REST API doesn't support this?  Is the REST API being deprecated?