Why are both mass and amount of substance the two most independent physical quantities?

To be honest, quality exists in all things, but we generally apply a large amount of it to gases (I use hydrogen).

Physical quantities are interconnected through equations that describe natural laws or equations that define new physical quantities. Therefore, a few physical quantities can be regarded as independent of each other, while other physical quantities can be defined based on these quantities or expressed through equations. These few physical quantities that are considered independent of one another are called fundamental physical quantities, or simply fundamental quantities. The remaining physical quantities that can be derived from the fundamental quantities are called derived physical quantities, or simply derived quantities. In the International System of Units, there are seven base quantities: length, mass, time, electric current, thermodynamic temperature, amount of substance, and luminous intensity. All other quantities in various fields of physics can be derived from these seven fundamental quantities through mathematical operations such as multiplication, division, differentiation, or integration. Molar mass is the ratio of mass to moles; it is a derived quantity, not a fundamental physical quantity. Length and time can also be related to speed.

Because they belong to the seven most fundamental physical quantities: length m, time s, mass kg, thermodynamic temperature (Kelvin temperature) K, current unit A, light intensity unit cd (candela), and amount of substance mol