Each entry contains explanations for why they are in a given category.
Fairphone due to having some online code activation thing for OEM unlocking. Bootloader of my FP4 has been unlocked for quite some time now, but if I recall correctly, this activation step was required for me to load custom ROM on it.
https://support.fairphone.com/hc/en-us/articles/10492476238865-How-to-unlock-and-re-lock-the-bootloader
https://shop.fairphone.com/bootloader-unlocking-code-for-fairphone
This website disappears, you can't unlock your bootloader.
That is why Fairphone is in Caution section.

Microsoft being in "safe" is a bit funny, and the explanation acknowledges that as well.
But it is there due to it containing only two Surface devices, which have easy and standalone bootloader unlock process.

Why? Do you think they should be ranked worse because the company is bad? Unlocking the bootloader on every Google Pixel I ever had (1XL, 2XL, 3XL, 4a, 5a) is completely trivial. It's literally just a toggle in the dev settings, zero issues whatsoever.

There's even an online flash tool for the pixels if you find all the standard adb tooling a bit too complicated or not to your liking. I'd actually put them in "safe for now" tbqh, but Fairphone stays in "caution" for using the online doohickey the other user mentioned.