It certainly defied my expectations. Chrome is the same. All I can think is that they wanted an inprivate window's tabs to share a jar and that then gets kinda

It certainly defied my expectations. Chrome is the same. All I can think is that they wanted an inprivate window's tabs to share a jar and that then gets kinda complicated with popping tabs into their own window, putting them back, flicking between those accidentally while dragging a tab, etc. Looking at the docs it appears that Safari gets around this by just having a separate jar per tab? On desktop at least, mobile appears to be shared.