They're quite different jobs also. Core Unity engine development and most of the tech jobs are in Copenhagen, while the SF office is mostly sales/marketing/accounting. It was kind of a half-move where they moved the "business office" to SF but didn't move the technical team. That happened years ago, initially mostly because of sales: having an "SF" company and a sales team based in SF made it easier to get in contact with the large customers who produced most of their licensing revenue (at least at the time).