Broker trade against you
Even though you are using similar assets, the style of trading is completely different. This goes for all types of trading; even if you are a pro day stock trader, you will still want to practice before you jump in headfirst with binary options trading. Some brokers require that you make a real money deposit before you can start using their demo account.
You dont need to trade with this money, but the brokers know that youre far more likely to.