When creating a page from a blueprint template (example: The Troubleshooting Article template), you will be prompted with a dialog box similar to this:

Entering the page title there will produce the expected results: the page title field will be automatically set in the editor.

You can't replicate this behaviour on a custom template though. Creating a "Page Title" variable in the template will trigger a similar prompt, but will not populate the page title field.

Please make it possible for us to replicate Blueprint templates' behaviour on user-created templates.

Partial Workaround 

Use the create a template macro 

Allows to customize the titles and offers variables @currentDate, @spaceName, @spaceKey

https://support.atlassian.com/confluence-cloud/docs/insert-the-create-from-template-macro/