To get access to the big banks, you would need to be doing some pretty heavy volume, ie $5M per month, so if you wanted the big 4 on your panel you would need to be doing in excess of $20M per month in loans.

So the aggregator sits between the broker and the bank, and the aggregator might have hundreds of brokers which combined would easily write the necessary volumes.

So a broker writing $2m of loans a month would be able to access a wider variety of lenders if they go through an aggregator.