Because it is curved and would require a great many primaries to approximate it, not to mention the enormous files resulting from that approach. Assuming that my edits in the quote are what Ed meant.
Only sort of. Your supposition implies that a normal capture will be dripping with out-of-gamut colors. I've already mentioned Pointer's Gamut and provided links. Did you take a look? Most colors collected within that gamut are also inside sRGB.I suppose that too many out of gamut colors would then be forwarded to the internet or printers...yes?
A useful app is ColorThink where the gamut of any capture can be displayed against several color spaces, 2D or 3D.