Non-MS people provide emulators for 16 bit on 64. The problem was that MS Dos box AKA the NTVDM was using CPU features in 32 bit x86 not on the x86-64, but DOSBox and other EMULATORS don't need any x86 CPU features, which means it works on x86-64 based OS, though the Windows version is maybe 32 bit.
It's simpler for MS to offer VM support for XP, Win7 etc and to ignore 16 bit because DOSBox has worked better for 16 bit, especially graphics and sound for over 15 years than NTVDM, which was really just for DOS text and as a backend for native 16 bit code for WOW for 16 bit Windows on NT, which never have great compatibility.
Current OS versions for DOSBox
Mac OS X 0.74-3-3 dmg (Universal)
Windows 0.74-3 Win32 installer
Fedora 0.74-3 rpm
Source 0.74-3 Source
Debian 0.74-3 deb
FreeBSD package 0.74-2 ports
RISC OS 0.74-2 zip
Gentoo Linux 0.74 portage
OS/2 0.74 exe (OS2)
Solaris 10 - sparc 0.73 pkg
BeOS 0.63 binary (x86)
From
https://www.dosbox.com/download.php?main=1
There are older versions for Symbian (ancient ARM) etc.
DOSBox is now included with WINE (at least the Win32). You have to set an environment variable on 64 bit Linux before installing WINE (add x86 Architecture) or only WINE64 is installed. Which is a bit mad, because WINE is mostly useful for 32 bit Windows applications, which don't run at all on WINE64