This might go better on academia stack exchange, but it seems probably the people who know the answer are on cross validated..
This is a pattern across the US. My classmates in, e.g., neuroscience PhD programs take only a few courses. The structure of the PhD is far more like an apprenticeship. Conversely, my classmates in PhD programs take on the order of 12 courses. (Computer science PhDs take about the same.) Why the difference?
Could it be that perhaps statisticians have to be prepared for anything? They might work on a project where a new clustering method is required one day and have to develop a hypothesis test the next?
Could it be that a student could technically have great insight and prove a theorem during the first afternoon of their PhD, so the coursework ensures that they stay at least a fixed amount of time? Experiments in neuroscience usually take much longer, so the PhD program is guaranteed to have the student for a while.