Gold is fairly common, yes and it's been somewhat staple in terms of cover art.
There are a few reasons for this in my eyes; one is that "Gold" is a colour that tends to be associated with the franchise a lot, it's definitely the stand-out colour or most significant -- the Triforce probably being a reference to the colour itself. Also, I see it as a neutral colour, if they used red/blue/green, then some may interpret that colour or associate with a certain race/element etc. while gold is more of a neutral colour and can represent the entire franchise.
It's possibly a marketing tactic too, they have the Zelda logo, but like any product; they need to make it stand out. Gold is a good colour to make something stand out and also; gold is a colour that tends to be related to quality and whatnot - Nintendo are probably trying to get across the message that this game is important and worth something to the consumer. The reason why this tactic is repeatedly done is because it's seen as successful and it's becoming a brand identity somewhat, people will now associate that colour with the franchise itself and therefore familiarise themselves with it.
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Obviously I'm looking a bit too deep into it, but marketing tends to focus on small details and whatnot. To be honest, I do think it's a worn out usage, I'd like to see more variety in standard box art covers, it's not that important to me, but I would like to see some new and unique covers for once.