Forgive me for my "ignorance" but I don't understand why the financial argument doesn't stack up.
Since we are talking hypothetically here lets assume a few things (and I'll use Dion as an example)
Let's assume he's been profitable for four years. In his first year he started with a small account as he had only just learn the ropes and he made $50,000. Second year he did very well, always upping his size and made $80,000 profit. Third year he made even more ; $130,000. Last year he made, lets say $150,000. The account would be growing steadily ; the performance would show clearly he is extremely profitable and making very good money by most peoples standards. That would be irrefutable.
Now lets say that he can develop some very useful software for traders. He charges $300 and it hits the big time and is bought in bulk by firms for their traders and locals all across the world. Lets say in his first year he shifts 1000. So he's made $300,000 (or double his latest and best year) for taking absolutely no risk and making some software he believes in and which he thinks can help people.
Assuming all the above elements are true, there's a term for this in business (and in trading) it's called a no brainer.
Naturally, the same theory could easily be applied to a trading room. If a trader takes 3 - 5 trades a week and spends the rest of the time sitting there watching the markets, why on earth would he not make a risk free return for filling empty hours? It's hardly difficult to talk on a mic and show people what you are doing.
Part of the reason people always ask this question is because they presume all profitable traders have the key to making millions which really only goes to prove one thing ; they clearly have no idea of how the market works.
I used to know an outstanding trader. His up days averaged around £1,500 and he probably had a down day, averaging around £500 once every two weeks. He was about 2 years into the game, extremely consistent and made extremely good money. He worked long hours and very hard too. He had some liquidity issues that meant that while he could continue to make that money he had temporarily reached a glass ceiling of sorts and his skill, whilst transferable to a larger market like the spooz was also going to take some time to implement and adjust too.
One day he said to me out of the blue : "I'm tempted to set up a website - it would be hard scalping live infront of people because of the pressure and I don't know if I could talk and concentrate at the same time but maybe I can record my day and talk over the top of it after illustrating what I did".
My first reaction was "probably not worth the hassle mate - you're killing it as it is". He just looked at me like I was the biggest f*cking moron to ever walk the earth and said : Get 200 people to join a website paying £150 a month and thats £360k a year for...er...recording some videos? You don't think thats worth it?
As I said, that was straight from the mouth of a highly profitable and excellent trader.
But it's hardly surprising is it? There's another term for it. It's called business. The question of why do vendors do it is so interesting coming from "traders" because as a trader, it's all about return (and let's not forget rate of it too, right?)
It actually baffles me why people ask it all the time!
If I turned this on its head and said to you "you're a web designer for a company and earn £100k a year. Would you take on 2 extra hours work per day to freelance outside your company and get well over a 100% increase on your salary, are you telling me you would honestly say no?"
As I said, this all presumes that the material shown is good, that the trader is profitable etc etc. But since you already presumed that, this is my answer.