If you want all the variant values to be selected by default, tick Auto Selection in the Product Variant group details.
The “auto selection” function is designed for banquets where you want to select all the dishes for that banquet at one touch of the button. The “banquet” itself would be the product, and all its dishes would be product variants.
It could also be used for highly customisable dishes where you want all the ingredients to be product variants that are selected by default, which can be removed manually.
Find out more about Product Variants