New York is becoming the ideal place not just for homegrown startups but for emerging european companies to call home. The city's robust financial eco system and the potential for larger deals are both incentives for companies to make the trip across the atlantic. Furthermore european entrepreneurs may prefer Silicon Alley over the west coast simply because its closer to the region. This makes running european based off shore teams easier as well as business travel home more manageable.
New York offers one of the strongest financial ecosystem in the world and a growing availability of venture capital. According to CB Insights New York companies raised $4.5 billion in venture capital last year across 422 deals while according to Dow Jones Venturesource, European venture-backed companies raised in total $8.5 billion across 1,460 deals. This means New York places more than half of Europe’s venture capital capacity. Furthermore, the average investment size in New York is about $11 million, while the average size in Europe is below $6 million – making New York City the place to be for later stage investments. A big part of the invested money derives from multinational companies. Accelerators such as TechStars are actively advising in corporate venturing and pushing this trend forward. Another advantage of the city is its powerful banking sector.
http://venturebeat.com/2015/04/04/why-new-york-city-is-the-best-choice-for-european-startups/