[ljw1001]

I think it likely that people with large-scale experience who aren't at Google would have lower tenures than average, simply because they're becoming more valuable and most companies don't pay people their replacement wage if they've been there very long.

[mmt]

The effect that you mention is already cited for the trend of lowering average tenure of technical professionals, in general, so, absent specific evidence that this subset's market value differential (market value less existing employers' willingness to keep up) is increasing faster than average, there's no reason to believe that's the reason for a shorter than average tenure.

We don't even know if the tenure is shorter than average.

Regardless, neither the primary motivation for a short tenure, nor even any average would be particularly meaningful with regard to what I believe to be ris's implied accusation:

Absent at least one tenure long enough to see through the consequences of the creation of the large-scale system, such a creator cannot be truly considered experienced with large-scale systems, no matter how many such creations are on the resume (even though the market values/hires the latter).