The single-threaded nature of WPA2 AES-CCMP-128 is the reason (in addition to not wanting to embed known weak security protocols). The higher speeds and later standardization of Wi-Fi 6E (as compared to Wi-Fi 6) made this, in my opinion, a reasonable trade-off.

For Wi-Fi to survive, it must bring improvements in security protocols /and/ user experience (speed, coverage, and ease of setup). While I agree that security configuration should ideally not be tied to the physical characteristics of the link, security tends to lag, and the driver is user experience. So, if we want to have a high baseline of security, we have to tie it to the driver, the craving for a better user experience (higher speed and better spectrum utilization).

Good standards make trade-offs in the right places (both in time and space). Dumb standards miss the goal. I cannot say that this is a dumb standard when it is evident that trade-offs have to be made. Using WPA2 would have impacted cost of equipment, performance and security negatively.