Solid color creation & Mask

An empty mask appears by default for all of the Fill layer types so that if you wanted to restrict the fill to an area, you can immediately start painting in the mask. The reason the fill color still exists when you delete the mask is because nothing has been painted into it yet.

I don’t usually mask off solid color layers, so I think having those empty default masks clutters the Layers panel. This is why Adobe makes them optional: If you don’t want a mask to be added to every new Fill type of layer, then open the Layers panel menu, choose Panel options, and disable Use Default Masks on Fill Layers. I have done this, and I like it better this way. If that layer needs a mask in the future, it only takes one click to add it.