How come rank 6 jets have the highest repair costs?

A few examples: (when stock)
G91s are 10k
everything french and swedish is ~9k
Israel is 8.5k or 9.5k
etc etc, average is about 9k
US averages about 10k with a few outliers like F4c at 11k

Meanwhile, most rank 8 vehicles don’t see over 8k, and there isn’t a single vehicle that sees 10k stock.