Why is Inflation so Low?

The Phillips curve tradeoff of inflation vs. unemployment is a triumph of narrative over data. Here's a graph annually from 1960. If the Phillips curve had any validity, this would be an upward sloping series of dots, more or less.

Well it obviously is not. In fact there is a very low statistical significance here, certainly not enough to make policy on. For those years with less than 6% unemployment, there's no relationship at all. So why does everyone believe it?
Because the narrative is compelling. Common sense tells you that if labor is tight, workers will be able to demand higher wages. The problem with this argument is typical of economics; there are a lot of confounding variables that interact in unknown ways. They screw up the relationship.
If an economist asked a data scientist to look at the above chart, he would roll his eyes. Data people are used to looking at relationships that have actual power. Now I know that it is possible to construct models using lags and intermediate relationships that have greater explanatory power.
I call this "theory mining." The space of possible models is essentially infinite. So if you try enough things, you will come up with a theory that explains the past. The future; not so much.
My view is that demographics and social factors are all in the mix. There's not enough variation in the history to tease this out of the data, but it's my narrative. It's no coincidence that the one episode we had of actual high inflation since WWII was in the 70s, when the boomers were starting families and jobs. Now it's the opposite. We are going to have a continually aging population for several decades. Now I love old people, but they don't buy much stuff. Either they already have it, they are on fixed incomes, or they have moved on to other facets of their lives. There's a reason advertisers go after the 18 to 44 age bracket.
Of course this is not just happening in the US. The whole developed world and much of the emerging markets are in the same situation. So I expect the world central banks are going to have keep interest rates lowish for longerish.
That doesn't mean commodities prices will stay low. The world economy is still expanding, and there's not enough investment going into basic materials. One of these days that is going to matter.