Why do Articles have Editor/Preview tabs but other documents don't?

There's a simple explanation for this! The Editor/Preview tabs you're seeing in some documents are not automatic - they're configured through the Structure Builder API using defaultDocumentNode.

By default, all documents in Sanity Studio only show the Editor tab. The Preview (or any additional tabs) appear when you explicitly configure them using the getDefaultDocumentNode function in your structure configuration.

Here's what's likely happening in your setup:

For "Articles" (with tabs): Your structure configuration probably has something like this:

export const getDefaultDocumentNode: DefaultDocumentNodeResolver = (S, options) => {
  if (options.schemaType === "article") {
    return S.document().views([
      S.view.form(),
      S.view.component(PreviewComponent).title('Preview')
    ])
  }
}

For other documents (without tabs): They're using the default behavior, which only shows the form editor.

How to add tabs to your documents

You can configure document views in your sanity.config.ts by:

1. Creating a getDefaultDocumentNode function that returns different views using S.document().views()
2. Adding it to your structureTool configuration:

import {structureTool} from 'sanity/structure'

export default defineConfig({
  plugins: [
    structureTool({
      defaultDocumentNode: getDefaultDocumentNode,
    }),
  ],
})

You can conditionally show preview tabs based on schemaType or documentId, which is why only certain document types have them.

For more details on setting this up, check out the Structure Builder documentation on creating custom document views.