A (very) key difference is that this behaviour is mandated by the FAA, and consistent across all providers. There isn't a (legal) option of just not-doing-it because it's "cheaper".

Modern companies generally do not have the same incentive to keep their SRE (or engineers in general) upskilled. Cutting SRE because "we don't really have incidents, why do we keep paying them? If we need to do layoffs I would rather keep a product engineer" will always* (okay, _generally_) be the direction that organizations go without external influence or requirements.

Now I am sure there are some companies or industries where this is required (for example, I would not be surprised if certain military software/services contracts had requirements for support staff with X hours or training/etc), but that is not consistent everywhere.

If we want something that is "money-losing" in the short/medium term to be consistently applied, it unfortunately needs to be (uniformly) regulated.