Also: the Carbon API set is only supported on 32-bit, and removing 32-bit means all of Carbon can go away. Carbon is a massive API set, with one or sometimes two full legacy APIs (often dating back to the 90s) for everything. Drawing (QuickDraw), multimedia (QuickTime), open/save dialogs (NavServices), fonts/text rendering (Font Manager, ATSUI), windows/menus/dialogs (both HIToolbox and the classic Managers), file I/O, printing, and on and on. Keeping all this stuff functional (to support old apps) while evolving the system underneath is a huge burden which will be lifted from 10.15 on.