From a planning perspective we use standard weights and each region of the world has a different weight for a male/female or ‘all adult’ standard weights. There are then set weights for children. This standard weight will also include an allowance for hand luggage. Statistical data is gathered by the airline and also the CAA periodically and trends in weights monitored to establish updated average weights.

We can split weight by M/F/C/I too if needed. There are separate weight schedules for charters too. This all takes into account the variance based on region and type of flights and thus the reasons people are travelling on that service and when they tend to travel with or without.

As to why? You’ve already highlighted the commercial proposition and attractiveness to many flyers.