Because there are orthogonal performance properties and making them all get “better” with a higher “performance” number would be very expensive. Someone taking photos wants high capacity. Someone taking 8K video wants high write bandwidth. Someone playing games or as phone app offload storage wants high IOPS.
It’s why yo can buy a 1TB low-IOPS card for $40, or you can buy a 256GB high-IOPS card for $40. But if you want 1TB with high-iops, you’re going to pay about $200.