Why does it matter if there is an overseas connection? It’s common knowledge that all of the overseas radical Islamic terror groups have sympathizers here. They don’t issue membership cards.
I guess the only reason it’s important is if it can be traced to state sponsored groups in which case we can send them even more money and resettle even more of their citizens here. /s
It matters because if they can’t find an obvious overseas connection, they can deny that it’s Islamic terrorism. It’s a lone wolf, or a pack of lone wolves, or wannabees, or mentally deranged, or disaffiliated, or rogue whatevers, or “self-radicalized”, etcetcetc/