They're already losing enough money with Marcus right now, why risk losing some more? Goldman needs to figure out how to properly run their existing consumer bank first.
Marcus is meant to focus on proper retail, which is a very different business to this. Buying SVB doesn't really achieve what Goldman wants from Marcus.
Because they do serve the UK, parent mentioned Marcus which is one of their UK consumer products. I don't know if they want to leave retail, but that's the sort of thing that can be different by region.