Yep, you’re right. I bought my GameCube new back in the day and it only came with the composite cable. The component cable is a separate purchase and Nintendo only sold it in Japan. In addition to that, the Digital A/V Output Port was also removed from newer GameCube models¹, lowering the probability of someone wanting the cable even further.

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¹ — https://www.nintendo.com/consumer/systems/nintendogamecube/c...