[TapamN]

It not necessarily physical RAM. If you memmap large files, like maybe a large file from RAID or network share, you could still need that much virtual address space.

[Dylan16807]

Do many programs want to use that much data but not control when it swaps in and out?

[wittystick]

No, but 5-level paging is opt-in anyway, so its presence isn't problematic if assuming a 48-bit address space. Linux won't allocate space outside the 48-bits unless you give an address hint to mmap outside the 48-bit range.