Hey - extremely late response/update on this, but I shipped a change for this a while ago. You can update the price of dev products on creator dashboard to null, which preserves the same functionality as WWW where it is no longer for sale. Let me know if you’re still seeing dev products available for sale with 0 cost after updating a product to a null price.
Now as to why dev-products don’t behave like game passes where you can deliberately set the pass for sale or not and not have a hacky workaround of setting the price to null, unfortunately I don’t have a satisfactory answer other than dev-products is rooted in very old, legacy spaghetti code. There have been talks