What's missing from this IMO is any explanation of why 5% is the magic number that makes this possible. If the socially beneficial aspects of local banking are

What's missing from this IMO is any explanation of why 5% is the magic number that makes this possible. If the socially beneficial aspects of local banking are funded by the spread between what the bank pays its customers and the market rate of interest (in the Federal Funds Rate/the 4 week t-bill/money market fund yields/etc) why does the spread have to be so high? Why can't the bank pay its depositors 3% and do this stuff with a 2% spread? A 5% spread is the highest in at least 15 years and local banks seemed to be doing fine throughout much of that period.