Firstly, any liquid cleaning product is made mostly of water. When water is added to a product for retail purposed, preservatives then need to be added too. For any liquid based cleaning products, we provide the glassware and ingredients, so that you can add your own water. This not only saves unnecessary chemicals coming into your home, it also reduced the weight of the item, costing less to transport.
In other cases, the kit may be designed to offer glassware so you can fill with ready made products or to allow you to fill yourself with the DIY ingredients.