I'd argue (but have no historical context) that it's a distinction between storage format and presentation interface, and IMHO that makes a lot of sense. A terminal has other operations too, backspaces and deletes being the most basic. Which coincidentally are one hell of a mess across different terminal types between ^H / 0x08 and DEL / 0x7f as well…
(And these distinctions predate UNIX — if I were confronted with an inconsistent mess I'd go for simplicity too, and a 2-byte newline is definitely not simple just by merit of being 2 bytes. I personally wouldn't have cared whether it was CR or LF, but would have cared to make it a single byte.)