I think "the market has already priced it int" and, "there is no where else to invest" are both good reasons, while the market will shrug off yet another warning sign.
My 3rd reasons, is that at least one of these two statements is true.
A. Central Bankers have become a lot better at using monetary policy, to dampen the business cycle swings and keep the economy growing steadily, since 2008
B. People believe A is true.
I will say since there are tens of trillions of stock market gains, it's very expensive to doubt the Fed's/central banks ability to handle things. So I'm quite confident, that the vast majority of money people will publically say B is true, but it is also possible so is A.
Regarding interest rates. A number of years ago, I read a scholarly paper by some economists on the historical interest rates and default rates of sovereign debt. Going back from roughly 1400, they determined that the historical interest rate on long-term (10+ years) was about 5%. They also found that countries, that haven't default on their sovereign debt are the exception. (The US, most commonwealth country, Switzerland (kinda of), and few of the newer democracies haven't. But, most of Europe, UK, pretty much all of Latin America and Africa, and much of Asia have at various times defaulted. They count a default as dramatic devaluation or hyperinflation.
If you think about it, 5% is a pretty reasonable risk-free interest rate, you double your money every 15 years, it more than historical inflation of 2-3%. Endowments, are supposed to distribute 5% of their assets. We all talk about the 4% SWR (which includes an inflation adjustment).
Why anyone would want to loan Uncle Sam money for 10 year at 1.8%, much less loan me money for a 15 year for a house at 1.875%, or Uncle Sam for 30 years for 2.07%, makes no sense. I've heard of Europeans get <1% 15-20 years mortgages, which is just crazy. But since, much of this debt ends up the balance sheet of central bank, it is pretty much ignored