Singapore-listed real estate investment trusts may not appreciate much more in price given their roughly 20% rise this year — but strategists said they’re still a

The 10-year Treasury Bill is paying a yield of 1.87%.  Why are investors buying the USA debt for this paltry return?

The US debt rating being “downgraded”, is a matter of the choice of the US congress, not an inherent inability to pay.  The US dollar is a fiat currency, and the world’s reserve currency.  All US debt is trivially repayable, simply by printing money.  So any “default”, is a mere matter of political choice (like Congress refusing to raise the debt ceiling, in order to fund a budget they have already passed).  The >$16T existing debt, had nothing to do with the creditworthiness of additional US debt.

That doesn’t mean that it is impossible for the US to default.  Only that nobody can force that default.  The US would have to decide that it wants to default, for some bizarre reason.  Hence, US Treasuries are as secure and reliable an investment, as is probably possible to find in this world.  Those who want safety and security, are drawn to US Treasuries.

As to the low yield, you need to understand that inflation is also very, very low, and likely to remain there for a long time.  What matters to investors is real yield, not nominal yield.  With long-term expected inflation at such low amounts, even small (guaranteed!) nominal yields are sufficient to generate investment interest.