Every time someone designs a product and add to cart, the design is being save as a new product in my store, why?

This is required to create new products while adding to the cart. Because the platform doesn’t allow dynamic price modification in the cart and every product comes with a new image (with customization).

These created products will not show in your storefront, storefront search or in google search.

Also, without a new product, it is not possible (in Shopify) to save the customization information (every customization is new) over a single product. These created products will be automatically removed after 1 month.

If you want, you can remove them manually, if you do not want to wait for the automatic removal.