Are you aware that the Zelda disk was was also gold coloured? (Though admittedly not so shiny as the NES cart.)
Zelda was originally released on floppy not due to the high cost of making cartridges but because it couldn't fit on cartridges of the time. (It came out before mappers became a thing for Famicom cartridges.) Games on floppy were not considered "cheap" but "bigger and better than could fit on a cartridge." They might also make use of the extra sound channel that the floppy disk system added and usually would allow game saves, which cartridges also did not do at the time.
For various reasons Nintendo decided not to release the disk system for the NES, and this is at least one of the things that prompted them to develop mappers (letting cartridges have more ROM) and battery-backed memory, both of which made possible the NES release of Zelda a year and a half later.
Chapter 5 of I Am Error by Nathan Altice covers the disk system and Zelda in fantastic depth, and is well worth reading, especially if you're not familiar with Famicom culture in Japan at the time. From the beginning of the chapter:
A blank yellow cartridge hovers above a faceted metallic vista, its planar surface stretching into an infinite gradient of purple and black. The cartridge rotates lengthwise and vanishes in a beam of radiance as a yellow diskette takes it place, now held aloft by slender fingers. “The gaming world is about to change from cartridges to disk cards!” an announcer exclaims. Disembodied hands reach into frame to demonstrate the connections necessary to join the Famicom to its new shoebox-shaped companion. “Dramatically better games will be at your fingertips!” the announcer continues, as a green-clad elf plunges his sword into an enormous unicorn dragon.¹
So went the auspicious television debut of Nintendo’s 1986 disk drive peripheral, the Family Computer Disk System (FDS), and The Hyrule Fantasy | ゼルダの伝説, better known in the West as The Legend of Zelda. Promising “three times the power” of standard cartridges, Nintendo’s disks were set to change the console’s future. PCs had benefited from the expansive, inexpensive, and rewriteable storage medium for many years, but for home consoles, disks were uncharted territory. The Disk System would be Nintendo’s first attempt to extend the Famicom’s storage potential and answer competitors who were introducing newer, faster machines.