Why, what’s the problem with everyone working off the same datum?
It’s a bit like magnetic vs. true navigation. I’m not the slightest bit interested in what the Earth’s magnetic field is doing in various places - I just want to get from A to B in the most expeditious manner.
Geometric altitude gets rid of many of the errors that plague pressure altimetry, like temperature, lapse rate, variability and not least, transcription. No need to know the surface pressure. What’s not to like?