Another angle.
Lots of discussion about acft weight here, and how it likely to be underestimated. Suggested solution has been to weigh the acft, which is difficult, expensive, and potentially inaccurate.
What about switching to actual pax wt? With the technology available, it would be quite easy to incorporate a weighing system where people checking in stand. That way, pax weights along with ALL the normally un-weighed carry-on baggage is also weighed. No extra time taken, because they are weighed as part of the normal check-in.
Would potentially increase safety, but would almost certainly decrease profit margins. Perhaps the accountants don't want this info?