You don’t keep more money in your trading account as one bad day will come to take all your funds.
We are humans so one point of time you will forget all your principles, control of your mind and systematic trading everything. One small wrong step can lead to big loss.
Because of one small position stuck, you will be biased with your position then try to recover add more and more positions or wait for your price then market gives movement to your opposite direction hence you will lose all your money. But if you have small money then you no need to control anything as you may lose very small money which you can recover in small time.