Answer is in the article:

[That would have been even more work, because there was at the time no infrastructure in Setup for having 32-bit-only components. (And then automatically uninstalling it when WOW64 was disabled.) And besides, all the people who criticized Windows 96 as "not really a 32-bit operating system because it has some parts in 16-bit" would use the same logic to say that 64-bit Windows is "not really a 64-bit operating system." -Raymond]