It's not useful to tell somebody it is constant without a way to make use of it. Without knowing how it's defined relative to other things we can't use it.

The thing about all the absolute physical constants is that they are almost all based on units defined relative to other things. Unitless constants (defined only as a ratio) are extremely rare (like the fine structure constant) - but even then you have to make up units to measure them (although you can still agree on unitless values with somebody else who chose different base units for measurements).

https://en.wikipedia.org/wiki/Dimensionless_physical_constant

Edit: the most obvious immediate reason Wolfram here is fully wrong is that Cesium frequency is defined as the frequency you measure when light of the correct energy/wavelength is emitted against the atom, to then measure the corresponding returned light of the right energy/wavelength.

To determine what that wavelength should be with your instruments you can measure things like the electric field and charges - which depends on units that are all defined relative to each other, and as soon as you start fixing some units (like when you have measured the energy state differential in the atom) then you will realize you have defined ratios between the units