• Because first-party table creation is an API-only feature
• Because you must build a custom architecture for automating table creation
• Developer resources are not required for creating first-party tables in AMC

The correct answer is: Because first-party table creation is an API-only feature

Explanation: Amazon Marketing Cloud APIs (AMC APIs) are a suite of REST interfaces for developers to programmatically access AMC features. AMC APIs are often used to automate or schedule query workflows, create custom audiences, facilitate scaled operations, upload first-party signals, and enable integrations between AMC and other systems.

Reference: https://advertising.amazon.com/API/docs/en-us/guides/amazon-marketing-cloud/faqs