In order for products to sync from your Shopify admin to Google Shopping, they need to fit a specific set of requirements. There is a guide here for product requirements from Google that need to be followed, as well as specific requirements for Google categories that your products need to meet. Could take a look at these and make sure your products adhere to the guide?
Also, can you let me know what information you see when you click on “View these products to see why.” ? This will provide more information about what exactly is not syncing for you!