I am wondering why, with the vast tracts of codepoint space available up in the wilds of Plane 15 and 16, why does everyone (MUFI, SMuFL, ConScript, SIL, etc) want to crowd down into the tiny PUA island carved out in the BMP?
I (generally) get the historical argument, but PUA-A and -B have been around since Unicode v2.0 (23+ years?)
Is there a reason / rationale here? Is there a general carving-up of the PUA that I'm missing?
What causes well-tempered typographers to avoid saddling up the font tools and venturing to the wide open spaces of the higher Plains?