This doesn’t sound like they’re charging extra if you’re over a certain weight, which is what a lot of people here seem to be assuming. Its data collection for future designs.
People are aware that you get charged for overweight baggage for health and safety reasons, right? Anything over about 20 kilos is too heavy for a single person to safely handle so they have to get two people to do it, which costs more time and money. I would be very genuinely surprised if a few dozen more kilos from overweight baggage and people would be enough to seriously impact a plane’s flight unless you’re on a small town hopper