Do Linux distros and BSDs recommend using the command line to set up bootable USBs because most machines should be able to do it without additional software?
That and verifying the checksum are the big reasons I can think of. I feel like for the most part though using something like balenaEtcher is so much easier.
While I agree that dd can be easily used, it still is a dumb command (as in its only purpose is to write and nothing else), which can result in some issues regarding validating the integrity of the installation, at least for a beginner.
Furthermore, it can be disastrous if you don't pay attention to what you type in, as it will happily overwrite anything you type in.
Also, I don't think that dd alone should be used as a backup, as it might result in inconsistent backups. The best simple backup system, no matter whether you are a beginner or an expert, are snapshots, and maybe using dd to backup those to an external drive to be sure.
The ISO file should be validated, and many installation medias check hashes.
it can be disastrous if you don't pay attention to what you type in
Valid point, even I get nervous when entering dd.
I don't think that dd alone should be used as a backup
Absolutely it shouldn't. I said primitive backups, which are not a replacement for things like snapshots. DD backups are space-inefficient, easily corruptible, and often result in broken systems.