I'd be surprised, first of all, if that advert only took one day to do. I'm willing to bet there was more to it. (not that that is the point, but just saying) Rehearsals, fittings, set up, filming, and so on. That was not one day's work.
Secondly, I didn't say that's what they DID do. I said perhaps. And it isn't daft. If the elder son is bad with money and is looking at a career in football, there's a possibility that he could be earning a lot of money. If he's not good with money, he needs a lesson. Working in a coffee shop for a small amount of money, even for a short time, might teach him that he's in a privileged position and make him realise that without his parents' backing, he could be working on NMW and trying to make ends meet, which perhaps will make him appreciate not only his life but any money he makes. I see no problem in them having him work a NMW job temporarily to teach him about money. Otherwise, he'd be relying on the Bank of Mum and Dad forever.
Maybe Brooklyn has absolutely no interest in modelling, as he is obviously interested in a career in football. Maybe Romeo really does have an interest in modelling or acting. Maybe they are both very independent boys that are looking to line up their careers while they are young, knowing that both modelling and football careers can have a very limited shelf life. Why does it matter that one does one thing and makes more money than another? Different children, different situations.
Maybe people are getting their knickers in a twist over nothing.
I too find this ridiculous stream of vitriol towards the Beckhams absolutely puzzling. I think they have a good work ethic, stay well focused on their children, and are capitalising on their skills and opportunities to make money now so they will be able to retire without worrying and still be able to support their children.