x11-libs/wxGTK requires more than 2Gb disk space. Reproducible: Always
Gb = gigabits.
Many packages require that much temporary storage. Would you like pkg_pretend() to warn about available disk space?
I have a note with 4 GiB RAM and a half memory area for temporary storage in-memory build. Compilation fails in this condition. There are not so much such applications indeed. Firefox, chrome, boost, llvm gcc are known examples.
Then don't build in memory. There is no way to predict how much memory will be required to build something. It varies between gcc versions and options, architecture, etc.