In Stock & Inventory Lots, why quantity is always 0?
To see the lots quantity you must open the Stock -> Locations menu and double click on the location you want to see the quantities. From there just open the Lots by location option and you will see the quantities of all the lots in the location.
While using Internal Shipment, user wants to see the quantities while adding lots.
Do you mean that you want to see the quantity in the search window when selecting a lot on a stock move?
If yes, I think it is a valid improvement which applies also on product. It will require to set the from_location in the context and use a proper list view with the quantity fields (just like we do for sale line).
Yes. While selecting lot in stock move, user should be able to see the quantity against that lot available in the warehouse/storage location.
This will simplify the process, for example in Internal Shipment, for the user to see the details in the list.