M.Qassas has already highlighted the limitation in his answer. But there is a workaround to it.
Click on the file tab in SharePoint Designer
Select Reusable Workflow (towards the bottom) from the given options
On the right side of the page, you'll have the option to associate the content type to your workflow enabled.
Refer below screenshot for reference.
You should be aware of the SharePoint 2013 workflow platform doesn't support associated workflow with a content type.
If you tried to create a new Reusable workflow using SharePoint Designer, you will note that the Content Type drop down list is grayed out as shown below.
The only available workaround is to use SharePoint 2010 workflow platform
Select the Content Type of Document Library while creating Reusable wf.
To get access to your custom column, press the image button(Associate Columns) on the ribbon:
Press ‘Select Site Column’ and scroll until you find your column created in Step One. Select it and press Ok (twice) to get back to the workflow design area. (Below is image of SharePoint ...
This can be easily fixed right in SharePoint Designer (2013). Open the site. View the List. View the columns in the list. From the toolbar, click view Read-Only Columns. Delete the offending workflow status columns. Pretty easy.
There isn´t a simple way of removing old workflow status columns in SharePoint. You would have to remove them by code.
See the following urls for reference, and how to solve it:
Create a text file in SiteAssets library or any other library. Ex: /SiteAssets/ReusedContent.txt
Add a Content Editor webpart to the page
Edit the Content Editor webpart
Update "Content Link To link to a text file, type a URL." with /SiteAssets/ReusedContent.txt
Export this Content Editor webpart and import it to all pages you would like to reuse the content....