Prop firms such as Apex, Leeloo and Bulenox allow you to trade multiple accounts simultaneously. Not all of the prop firms allow you to do so. You need to have NinjaTrader platform and good trade copier.
It takes the same effort to reach your profit goals on one account just as it would take you with multiple accounts using trade copier. Same effort but outcome is exponentially doubling. Most traders use multiple accounts because they want to spread the risk.