Tesla autopilot / FSD is immensely more capable than 99% of LKAS systems, so maybe that's why regulators care more. But from a pure attentiveness standpoint, 1000 other car models have grossly worse safety in this regard.
However, my argument is that your original claim that the "L2 driver assist system must ensure that the driver is always actively supervising" is demonstrably false, given that, by pure numbers, "Level-2" capable cars, by large, do not have driver monitoring features. However, the government continues to focus solely on Tesla.
According to the NHTSA, Tesla was forced to enable driver monitoring via a camera because sensing driver steering input was insufficient.
So, without a doubt, 10s of millions of cars have "insufficient" driver monitoring while having "level 2" capability. Should those cars not be recalled and the feature be disabled (or updated to more aggressive monitoring if appropriate hardware exists)?
To be clear, I fully support driver monitoring for ADAS to whatever extent regulations require. But picking and choosing who to enforce the rules suggests they aren't working for the general public's best interest.