Since the distance and routing to DOH from SFO is very similar to that from LAX and may be extended and perhaps approaching the operational limits of the aircraft under certain circumstances, it is also possible that similar on-the-day weather, load and/or other rerouting issues may have affected this particular flight. And if that is the case, the airline may feel justified in identifying and charging those who are over their total allowances since weight=fuel=money. Checked in bags are all weighed so those are easily caught, which makes hand baggage offenders the obvious target.

If this was happening on every flight from every airport I suspect there would be many many more reports of it on here, so I’m not sure it's a blanket policy everywhere.