Why Prophet over ARIMA for ecommerce?

Three reasons. (1) Holidays, Prophet has a first-class holiday regressor with country presets. ARIMA needs you to hand-encode every holiday as an exogenous variable, which gets brittle. (2) Multiple seasonalities, ecommerce demand has weekly AND yearly patterns. Prophet handles both natively; ARIMA needs SARIMA + careful order selection per SKU. (3) Defaults that work, Prophet ships with sensible priors. ARIMA needs ACF/PACF inspection per SKU, which doesn’t scale to a 5,000-SKU catalog. ARIMA is still the right pick for stable, single-seasonality B2B SKUs, just not for the typical Magento mix.