MN 72 - Why is a freed mind not "not reborn"?
Well then, are they not reborn?
Tena hi, bho gotama, na upapajjatī ti?
‘They’re not reborn’ doesn’t apply, Vaccha.

I would suggest it has to do with the way this question is formulated. It's not about rebirth having ended but about pointing to a person because of the use of the word 'they'.
Talking about a 'they', 'him', 'her' doesn't apply anymore. So, the question is wrongly put.
That's my take on it.