f stop: why is not glass transparency part of the exposure calculation?

The number F is a ratio calculated exclusively from the focal length of the lens and the size of the aperture. Any light meter speaks in terms of F, Shutter and ISO.

A different glass, or simply a different number of elements, will change the number of photons that pass through the lens; we compensate the ND filters by adjusting F. What am I missing? Why is not part of the exposure calculations stopped?

In other words, I know what the T numbers are and how they differ from the F-stops. What I do not know is why portable light meters and related tools do not have provisions to take into account T, but only speak in terms of F.