Theory: Brussels — as the workplace of many “EU professionals” — has a large population of people from all over the EU (diversity and away from home), most of them fluent in English (good for mixing), and all of them working in a social/bureaucratic atmosphere (personal relations and “mixers”) are common. This seems quite the formula for an active dating scene in comparison to, say, Berlin or Barcelona (cities dominated by the “youth” dating scenes).
Data: I don’t have any. Do you? (Even anec-data are welcome 🙂
My one-handed assertion is that “nature will find a way” 🙂