Backward Compatibility: Updating the codec would require replacing or significantly modifying the hardware in all existing D-STAR radios and repeaters to work with the new standard. This is not practical, as it would render older equipment obsolete and split the user base, which goes against the goal of a widely adopted amateur radio standard.
Hardware Implementation: The AMBE codec is implemented as a physical chip (ASIC) within the radios. This requires a hardware change for any update, not just a software update, making an update a complex manufacturing decision rather than a simple firmware patch.
