'Oracle of Seasons/Ages' had nothing to do with Zelda either... or Ganon(dorf) for that matter..
Well, those weren't developed by Nintendo themselves but by Capcom/Flagship but
Zelda and Ganon appears when you play the other game with a linked save.
I could say that games not set in Hyrule had the excuse of not featuring Ganon nor Zelda such as
Phantom Hourglass being set after Ganon was turned into stone by the Master Sword and happened in a parallel world that explains why Bellum is the antagonist in this game.
Minish Cap being an exception yet this one is also explained by the fact it's set before Ocarina of Time so that the Thief Ganondorf wasn't there yet (or at least that the Gerudo King never heard of the Triforce up to that point). Said game also not being made by Nintendo's internal team either.
Also in 'A Link to the Past,' aside from the very beginning of the game, Zelda is no more important than the other 6 maidens that are sealed away in crystals..
I'd argue that it was a showcase of early-installment weirdness as this entry focused on the Sages' descendants since it had introduced them to the lore (although Zelda herself was still important in both NES titles).
It's almost like calling Final Fantasy "The Legend of Cid"..
I kind of disagree because Cid was just being a recurring secondary character with a similar role but not the reincarnation of a divine power. The closest would be that in many entries there's a female protagonist important to the plot (like Terra, Aerith, Yuna and others I forgot about) but almost every FF games are set in a different world (aside from the ones set in Ivalice and direct sequels like X-2) so it's not really equivalent.
I could agree that The Legend of Zelda could've still been called "The Myth of the Triforce" and it wouldn't have affected the franchise that much but Legend of Zelda still gives a cooler sound to the ear and she's still one of the three parts of the Triforce even if her physical being isn't involved that much in the games. This is about the
Legend after all.
Yeah... And... So?
Plus, all of the "Legend of Zelda" sequels/prequels/requels have subtitles. The only one that was numbered 2nd NES game, and it had a subtitle too: "Link's Adventure"..
Zelda II is the black sheep of the franchise in more than one way, almost as if the numbering was a way to further the oddity of that entry (aside from ALBW being called Triforce of Gods 2 in Japan for some reason but I'm glad they didn't name it "ALTTP 2" in the west).
Two of those at the beginning are side/gaiden games anyway. Which explains the subtitles for either game, and makes sense.
Not being made by Nintendo directly and being focused on two of the Goddesses (Nayru and Din) could explain it (although I still regret the lack of a game focused on Farore).