The pack.mcmeta file is required for Minecraft to recognize the folder as a resource pack. Since the file inside the vanilla JAR uses specific internal versioning, the system should ideally this file to ensure compatibility with the user's current client, or use a standard template:

Whether you need a clean template for a custom project or want to restore the original look to a modded game, here is the complete guide to obtaining and using Minecraft’s default textures. How to Get the Default Texture Pack (Java Edition)

Allows users to download the vanilla (default) Minecraft texture pack directly from the application. This enables resource pack creators to use the default assets as a base for their custom packs without needing to extract game files manually.