Just bad strategy, GDDR6 is expensive. last I read it cost 11.60usd per 1GB chip for 14gbps GDDR6
https://www.guru3d.com/news-story/gddr6-significantly-more-expensive-than-gddr5.html
1660 with GDDR5 still beats 5500XT, that means equipping these cards with GDDR6 is kinda pointless. Or maybe because Navi still lack the compression technique that Nvidia employ, thus requiring bigger and faster VRAM to compete.
GDDR 6 might be cheaper now, AMD is charging 30usd for 4 more GB. Techpowerup inspected the PCB and mention that it is overengineered for this kind of performance bracket. So overall bad decisions were made over at AMD.