So unfortunately people do care, it's why 32bit windows is still a thing. Most of the people that care however are large legacy enterprises that are running line of business applications that they don't have the source code for or require libraries they don't have the source code for. While they are migrating it's not a quick process in many cases.

As for 16bit HANDLEs for 32bit programs, it wouldn't have solved the issue as the HANDLEs are kernel tokens. The kernel doesn't actually care whether the user space application is 32 bit or 64bit in many cases. That's all handled via WoW64CPU.dll and friends. They proxy all kernel calls from 32bit code and then segment switch to a 64bit segment before calling the kernel. The same happens in reverse when coming back. So it would incur significant performance overhead in many cases to add that when it isn't really necessary and would negatively impact already memory constrained programs. Instead MS chose to let them get the best benefits they could from 64bit mode: all 4GB the 32bit address space can be used for 32bit things instead of just the bottom 2/3GB (depending on being flagged /LARGEADDRESSAWARE). In the end it's a lot more complicated than just telling people that aren't using very memory intensive apps in the first place to just run 32bit Windows which already works... and supports vm86 mode.