$ pacman -Si apt
Repository : extra
Name : apt
Version : 3.1.4-1
Description : Command-line package manager used on Debian-based systems
Architecture : x86_64
URL : https://salsa.debian.org/apt-team/apt
Licenses : BSD-3-Clause GPL-2.0-only GPL-2.0-or-later MIT
Groups : None
Provides : None
Depends On : systemd-libs libseccomp perl xxhash dpkg gnutls bzip2 sequoia-sqv xz gcc-libs lz4 bash zlib zstd db libgcrypt glibc
Optional Deps : None
Conflicts With : None
Replaces : None
Download Size : 2.63 MiB
Installed Size : 8.24 MiB
Packager : Alexander Epaneshnikov <alex19ep@archlinux.org>
Build Date : Mon 11 Aug 2025 08:52:43 PM CEST
Validated By : SHA-256 Sum Signature
https://archlinux.org/packages/extra/x86_64/apt/
I would guess they’re there mainly for developers on arch cross developing for those distros. Not managing packages on arch.
e.g. I install rpm on arch but only use it to build rpms.