SharePoint - Save as Site Template for Publishing Site
SharePoint publishing sites by default does not allow you to create site templates.
A quick fix for this OTB is as follows
1. Open the site in SharePoint Designer and in the ribbon , under Site Options, look for SaveSiteAsTemplateEnabled and set this to true value.
2. Open the site and_layouts/savetmpl.aspx. Or. /_layouts/15/savetmpl.aspx.
3. Save the site.
If the saved template is not showing up while creating sub site then go to the site settings and into 'Page layouts and site templates' and add the requested site template to the allowed list of site templates.Now it should be ready to go.