-Zelda, BotW (translation source: myself with help from a few others)Hero of Hyrule chosen by the demon-bane sword, in recognition of your devoted effort and fully-developed swordsmanship, I grant you blessing in the name of the Goddess Hylia. The bonded blade is together with the hero's spirit, whether dancing in the sky, travelling through time, or dyed by twilight. I pray so that further power lodges in you and also in the demon-bane sword. Demon-bane sword born in a distant past, you who bring blessings to Hyrule alongside the hero, I grant you blessings in the name of Goddess Hylia. Across the seas, in the time of need of the god-made gold, may you appear alongside the hero. I pray so that further power lodges into the demon-bane sword and the hero of Hyrule.
With this bond between the hero and the sword in mind, let's re-examine a few quotes from WW:
-Laruto, WW (translation source)Unfortunately, the Master Sword you possess has already lost that power due to Ganondorf's strategy.
When Ganondorf, who had been destroyed by the Hero of Time, was revived to Hyrule, he attacked this temple and took my life in order to erase that sword's power. In order to restore the anti-demon power to the blade, someone to pray in this temple in my stead is needed.
-WW intro (translation source)Again, a calamitous storm began to blow across the kingdom.
The evil one who seemed to have been sealed away by the hero
crept forth from the depths of the earth.
The people of the kingdom believed that the Hero of Time would appear a second time.
But the hero did not appear.
Faced by evil forces, they were at their wit's end, all they could do was pray.
Finally, they decided to entrust their fate to the gods themselves.
I believe we finally have a definitive reason why the hero never appeared in WW's backstory. It's because Ganon weakened the MS, and he did so because he knew that would prevent the hero from appearing.
Further, the MS still being in its weakened state is why WW-Link isn't regarded as a hero until he proves himself at the TotG. Most other Links were predestined to be heros which is known by certain NPCs in their respective games. Only WW goes out of its way (e.g. KoRL & Jabun) to insist that Link isn't the hero. There's no "true" hero because there's no "true" MS.
This may also be why the hero does appear in the alternate events (LttP) on the decline timeline. Ganondorf wasn't defeated by Link in that timeline, so he doesn't learn to fear the MS (or the hero), and doesn't remove its power when he returns. So with the MS at full power, the hero also appears and LttP happens instead of the Great Flood.
"But BotW takes place far in the future and/or on a different timeline." - The blessing is said to imitate an age-old blessing from Hylia. And like Demise's "curse", I believe it's more a statement of how the world works (and has always worked) than some sort of spell or prophecy.