That’s just like bankroll management in gambling. For OP, if he starts with $20,000 for trading, he’d only risk $200 per trade. It’s basically the amount he’s comfortable losing on each trade.
That is a good risk management. To be using just 1% of his trading fund for trading. Even if he loses the money, he will not be thinking about the losses just as it is in gambling.
And, as it was said, it may be the fees that are working their magic, basically.
It could be the FedEx especially if he is a scalper. I do not know about forex but if it is an exchange, using an exchange with low fee charge will be better. Also he can set TP limit order which would be of lower fee charge.