The answer is probably profit margin. It's also not unusual at all for Nvidia to leave performance on the table in terms of production nodes. I mean just look at the RTX 3000 series which was made with Samsung 8LPH, categorized as a "10nm node". Even at the time, for a late 2020 launch, TSMC already had several generations which were better, in both the "7nm" an "5nm" categories.