if I understand your question the reason is if you have attributes the customer must choose an option. The products list shows more info so the customer has to go into the product info page to select the option of their choice. If there are no options for an item then the products list allows the customer to quickly add a product to their cart. You can set the option in admin
Configuration -> Product Listing -> Display Product Add to Cart Button (0=off; 1=on; 2=on with Qty Box per Product)
set this to 0 and all products should show More Info...
Hope this is what you were looking for