Earlier quoted context omitted.
As a kid I made over 4% APY interest on my savings account. Risk free. Yes, I realize their are important differences here but I don't think that getting a 4% risk-free return should be seen as an "obvious" problem.
It's not about the exact percentage, it's about it being significantly higher than the risk-free interest offered elsewhere in the market (which is <1%). That's a big red flag that it's not actually risk-free.
I have zero insight into that. A lot of people seem to take it foregranted that existing bank systems are infallible. I have no way to assess that beyond the test of time (which is still worth something).
Cryptocurrency lending platforms have similar types of risk: what’s the feasibility of the thing being hacked. For most of these, I can actually do a very rough assessment because the code is public, the team is usually public (and has a track record) and there are probably some security audits by groups who either are or aren’t yet reputable. I have more tools for assessing risk.
So yes, some people will judge the risk of the 0.1% system to be lower than the 4% system. Some people will judge the risk to be the reverse (more practical if you substitute Compound/Aave for the 4% system). But you can’t separate the risk of a system from the users of that system so cleanly. There’s a very large subjective component to it.