[chroem-]

> The unanswered question here is why Prophet is so popular, and this surely merits a better explanation than I have given.

It has been explained by several posters. The goal of Prophet is to make time series accessible to non-experts, and the alternatives to Prophet are significantly more complicated. I say this as someone who has done pretty extensive work with time series for BigCorp's chain of retail stores.

[microprediction]

A moving average is not complicated. A moving average is more accurate. So I don't believe it has been explained in this thread at all.