The weight restriction for baggage handlers is much higher than the limit most airlines impose. As I already mentioned ~32kg is the Max weight for that.
I know that - hence using the term 50kg. As you've already correctly pointed out Business Class tickets usually have 32kg weight limits and you can purchase additional weight as an economy class passenger - up a maximum of 32kg.
I don't have an issue with this - as an economy class passenger. More weight = more fuel = more cost. I'd rather the minority that want more weight pay for it separately either through an excess charge or a higher class of cabin than have it factored into the regular ticket price. I don't need more than the 23kg I get, therefore I don't want to pay through my ticket price for a higher allowance.
The way it works for baggage seems fair, transparent and reasonable. The elephant in the room is the weight of the passenger and whilst it's technically very easy to solve this I can understand why most airlines are very reluctant to take the step, the fall-out and debate it would cause probably isn't worth the aggro.