The cost of more pins is linear in the number of pins, and the pins aren't the only component of the manufacturing cost, so a card with twice as many pins will have a manufacturing cost of significantly less than twice that of a card with half as many pins.

Cards with 16GB of VRAM exist for ~$300 retail.

Cards with 80GB of VRAM cost >$15,000 and customers pay that.

A card with 80GB of VRAM could be sold for <$1500 with five times the margin of the $300 card because the manufacturing cost is less than five times as much. <$1500 is unambiguously a smaller number than >$15,000. QED.