What prevents these projects from building on a 64bit OS with a 64bit compiler? Isn't that the simplest solution to getting rid of the ceilings rather than to continually restructure?
There is no x64->x86 cross compiler with MSVC, so if you want to produce i386 binaries you have to fit under 4GB of memory no matter what.
True, but you may be able to compile with the x86 compiler and link with the 64-bit linker.
I'm guessing they have to switch the build toolchain, and its automated, so they have to make a decision before asking IT to do so. (again, its a guess)