I'm curious about the directory layout in LFS. Why can't we use lib64 as the default directory in LFS if LFS is a pure 64 bit system?

Question

In Linux From Scratch during the 1st pass of GCC we have a case command that changes -m64 to ../lib instead of lib64. I am aware that this patch is to eliminate a compile time error but why can't we set the -m64 variable to ../lib64? I am also wondering about the LSB compatibility symlink on glibc in chapter 5. There is also a hardcoded path in ldd that we fix after the install of glibc. the path points to /usr/lib. We patch the ldd to point to /lib but we set the default directory path for our libraries to /usr/lib during configure. I am aware of fedoraprojects usr/move and how the developers have been working on the start up of the boot loader. So we put everything in /usr/lib /usr/bin and /usr/sbin. I guess my confusion is why we can't put libraries in lib64 on LFS if LFS is a pure 64 bit system. I am wondering if they're any 32 bit libraries that still come with glibc or 32 bit legacy programs that we build in blfs even though lfs is a pure 64 bit system and that is why we cannot use lib64? Any help appreciated. GLAWMAN