late in Tolkien's lifetime, when he was trying to square his own legendarium
with Roman Catholic orthodoxy. And you skipped an important footnote:
"Few Orcs ever [surrendered] in the Elder Days, and at no time would any Orc
treat with any Elf. For one thing Morgoth had achieved was to
convince the Orcs beyond refutation that the Elves were crueller than
themselves, taking captives only for 'amusement', or to eat them (as the Orcs
would do at need)."
Emphasis added.
Thus Tolkien explains the absence of orc prisoners, let alone reformed
orcs.
“I dislike Allegory - the conscious and intentional allegory - yet any attempt to explain the purport of myth or fairytale must use allegorical language. (And, of course, the more 'life' a story has the more readily will it be susceptible of allegorical interpretations: while the better a deliberate allegory is made the more nearly will it be acceptable just as a story.)” (From Tolkien Letter # 131.)
