WRONG!!!! Your sister was kidnapped as Ganondorf was pretty much capturing all the younger girls in hopes that one of them is Zelda. It is the leader of the pirates, Tetra, that was Zelda.
I fixed that 20mins before you posted. Come at me, bro?
Honestly though, only the younger and new players don't know who Zelda is. I mean, as a kid, I would name my character Zelda then get confused when the princess was Zelda. In fact, it was Super Smash Bros that made me realize he had an official name. Keep in mind I wasn't a big internet user back in the day.
That's because the older players have come across the real name of the character in several other places by now, such as the internet or other games as you did. If people that are picking up their first game of the series don't get it, there's probably a problem.
You missed the fact Link does like 70%-90% of the work in every game
I was confused with the first part here, you could say that's the main reason Link should be prominently named.
The main point is the whole story/legend revolves around Zelda. She is the key to all of it. The Hero, who is only named Link by default as he is "linked" to the player and can be named anything the player wishes, just ties the loose ends, acting as the Hero to set all the wheels in motion. It is Zelda who comes from the long line of the Royal Family and has ties to every creature and person in Hyrule.
The same could be said about all of the other human controlled heros in other media. The explanation of "link" you bring up is a good point, though. I might be wrong, but I don't always remember having the option to name Link whatever I want in all the games. Also, that doesn't change the fact that Link himself is the name of the character that has gone into popular culture; no one ever talks about the unnamed Hero of the series.
Also, Link isn't mute. We just don't hear him talk. For example, an owl asks you if you want him to repeat it again, you say no, the owl flys away.
I know, I was just seeing if I could enrage any Nintendo fan boys since none of their characters speak directly.