excellent arguments. However, attack sophistication is typically a response to environment. That’s the case for information security, state security, security in public settings, etc.
It may therefore be necessary to understand whether Belgium was the “low hanging fruit” most suitable to test “pilot attacks”, or if Belgium was the only target that a poorly-educated, ill-financed, uncoordinated organisation could pull off an attack against.
I believe the second is currently the case, but organizations evolve (sometimes).