Why aren't mass and size physical properties of matter?
The physical properties of matter are uniquely distinctive characteristics which can either be measured or observed without changing the composition of matter. Some examples include density, solubility, melting point, boiling point, polarity, etc. These characteristics can be used to distinguish one substance from another substance.
The mass and size of a physical body are quantitative measures which describe how many atoms or how much space is occupied by the body. Since these measures are not uniquely distinctive to the substance under consideration, they cannot be treated as physical properties.