retirements these days can last 20+ years (65 => 85 or earlier if wealthy). Federal Reserve mandate means your money loses significant value every year if stuck in a savings account. i am not aware of savings accounts paying 3%+, even bonds don't return that YoY. yes you may "avoid" losing 20-30% in one year, but those tend to come back quickly; with risk averse investments you're just stemming losses, not breaking even.

also see cFIREsim for an idea of the math: you're basically guaranteed to run out of money if you try to park in safe havens and you end up living a fair bit after you retire.