For one, they're providing the opportunity for you to open this business. That they have a bank willing to underwrite that type of account is significant.
PayPal, Stripe, and just about everyone else in the payment processing industry, will not work with you at all. Aggregating/factoring payments on behalf of others is prohibited in their terms/merchant agreements... because it's extremely financially risky to run such a company.
If it's not obvious to you why that is, you should consider picking up a cofounder with experience in online fraud/risk management. Managing fraud/risk is a core competency of every third party aggregator that survives its first few years. It's the reason PayPal is here today while their many earlier competitors went bankrupt.