Imagine you are in a commercial bank.
You onboarded a savings product.
It promises good ROI that is too good to be true. Maturity at a fixed time frame.
What must the bank do?
Earn a differential from the depositor-borrower rate
Invest funds that can earn it a higher ROI.
What if its investments is lacklustre?
What if its borrowers presented NPL
Etc ?
If the bank borrows or issues bonds, it will have to eventually repay. There is also the issue of credit rating.
If the bank is dominant and a monopoly, it can at its whims and fancies, delay the maturity of your savings product.
Instead of 5 years, it can now promote 7 years. Through creativity, it would invent an add-on with higher payouts to entice the depositor's delay for withdrawal.
It may also encourage you to delay your withdrawal and further invest your savings in more new schemes under the bank's ambit.
Essentially kicking the can down the road till an upturn in investment returns and reduction in NPL.
Or it has super duper fund managers like those in the Norwegian Pension and Oil Funds.