It seems to be a behaviour particular to portable devices. I'd argue encryption by default is a good thing on a device that's more likely to be stolen (and the identity theft implications that brings) but clearly it needs to be better communicated to the end user.
I reinstalled windows 11 recently and had to manually re-encrypt the boot drive, which also prompted me to save a copy of the key. I had the option of backing up to my MS account, saving a txt file (which it refuses to let you place on any encrypted drive, even if it's a different one to the one you're encrypting at the time), or print it (which can be to a PDF you can save anywhere). It's possible to access the backup options at any time after that as well. I usually take the last option, save the pdf to the same drive then copy paste the key into my password manager then delete the file.