The biggest chunk of their development team is still in Copenhagen (and the rest is scattered all over the world, with little actually happening in SF). You can't beat SF/SV when it comes to funding and networking with the industry. But when it comes to actually hiring engineers, Copenhagen still offers a big pool of highly skilled people with fewer other interesting jobs to choose from. It seems the optimal strategy is to develop in Europe, but have a sales/management presence in SF, maybe even officially re-incorporating there, even if it's mostly a front.