[giantrobot]

That might have been good enough for 1998 but I don't think it would have been as workable in 2008 and later in 2018. Remember without acquiring NeXT they wouldn't have also gotten NeXT's engineers and management. Apple obviously had management issues in the early 90s. The management that led to the failures of Pink/Taligent and Copland wouldn't have suddenly built a great OS just because there was a Unix kernel underneath. Hell, the best Mac development APIs came from third parties (Symantec then MetroWerks) rather than Apple themselves.

Win32 is a bit different than Toolbox/Carbon. For one Microsoft had superior first party development offerings. The best development tools on the Mac were from third parties that were increasingly disinterested in the platform. Windows was also an order of magnitude larger of a market. An ISV suffering through the pain of Win32 had a huge TAM in front of them. They could be profitable by only reaching a small fraction. An ISV targeting the Mac platform had a much harder time breaking even to say nothing of profitability just due to the size and nature of the Mac market.