Wait, why is it a Legend of Zelda if there's no Zelda? Eh, whatever.
Now I'm wondering if Maya played that game in universe. May have inspired her to collect masks.
for majora's mask and several others it was a marketing decision, they didnt think consumers would recognize the game as part of the series unless they put it in as part of the title, zelda isn't in every game
it was also the first direct sequel in the franchise (to orcarina of time which did have zelda in it) and technically... zelda is in this one as a flashback in the opening credits and thats it
almost all the games function on the premise of the hero's and villians reincarnate every thousand of years or so between games allowing for massive changes in landscape and locations and such. in addition to a broken multiverse spawning from the actions of link in orcarina of time