"The" is uncapitalized in the party list when casting certain spells.

[Rongway]

It's likely a style guide rule. The game tends towards minimal capitalisation, especially in the text log.

That said, I feel like "The End" at least should be deserving of an exception.

If it is, they should change that style rule. It would be strange to rule that "The Thing" in a cast bar context should be styled "the Thing". In the middle of a sentence, sure. But stand alone? No.