It might "just" be the homeless population is ageing. We really need a model prediction of how we expected the homeless population death rate to change over time. I doubt it is in a steady state.

"The number of Californians 55 and older who sought homelessness services soared 84% between 2017 and 2021" (from the article), so something demographic is changing. It'd be interesting to know what happened to their retirement savings.