Q: Why sku fetch is not showing the main image into my listing description?
A: Be sure you've not modified your sku fetch template because it needs the main image tag {{main_image}} on the front end of the template. Originally it was there within the HTML code already and putting the tag on the front end will just cause a URL to display as the tag simply inserts an image URL wherever it's placed... it has to stay in the source code.
To fix, please go to your template settings and click the blue reset template to basic button. That should set it back to its original format. Then save settings.
You should see a broken thumbnail image where the image is supposed to go. That is normal. Since you haven't loaded a url at that point, there's no image to display.