No 16-bit Code Can Run
When you try to run a 16-bit program, the application compatibility layer looks at the program and says, “Gosh, I wonder if I recognize this program.” And maybe the answer is, “Yes, it is InstallShield version 5.0, and I have been taught very specific information about the data files that are used by that version of InstallSheield to the point that I know how to install them without actually invoking InstallShield itself.” In that case, instead of playing a sad sound, the kernel hands the request to the application compatibility engine with the instructions, “You take care of this.”
Wow. Talk about going to extreme lengths to maintain legacy compatibility!
Also a reason there's so much cruft on the Windows side, and why the baseline that the majority of software vendors still count on is Windows XP.