I have never given this much thought, but is there an upper character/word limit in Bitcoin for passphrase lengths? I am asking because you said you use 12 words as passphrases. When I configured my Trezor with passphrases, I noticed that the device has a limit of 6-7 words (depending on the length) It seems it's different wherever you look. It's probably a memory limitation of Trezor, preventing users to set up longer passphrases.