Earlier quoted context omitted.
"Putting money in a jar" is a very handwavy way of addressing the problem of saving billions of dollars. You don't just put billions of dollars in a "jar". In practice, amounts that large have to be invested in some way. If you rule out federal treasury bills, what does that leave? State and municipal bonds? Pretty tricky (you could make a case for it though). How about stocks? No, that's de facto nationalization of…
Why do large amounts have to be invested? Is it because of inflation or large amounts of money cannot sit around without someone wanting to touch it?
The above is roughly how the system works now, makes sense right?
Of course, you'll see various peopl with an axe to grind calling it a pyramid scheme for the pass-thru payout. And claim that the government is "raiding" the trust fund by selling it t-bills, or say that the trust fund is backed by quote "worthless IOUs". I didn't know t-bills were so disreputable! But aside from the silly rhetoric, it's a pretty sensible strategy.
It shouldn't be a surprise that the people who administer the program 40 hours a week actually kinda know what they're doing. Unless you come to the conversation pre-equipped with ideology and blinders.