At some point there used to be electric typewriters with a 1 or 2 line buffer that they'd show on a black and white LCD. I don't know whether they had a spellchecker, but it wouldn't be hard to add one.
Except, you'd need ~50KB of ROM to store an English dictionary. This figure comes from the original UNIX spell program, which employed advanced compression techniques to fit into a 64KB memory footprint: https://ieeexplore.ieee.org/document/1095395
It would if they didn't have sufficient compute, RAM, ROM.
Something that can buffer and edit 2 lines (~160 byte, and not necessarily 8-bit ones either) does not necessarily want to add hundreds of kilobytes of dictionary and the code to look things up in it.