There have been plenty of extremely well organised, sophisticated and technically competent terrorists. The IRA, the Red Amy Faction, the PLO and Black September, Al Qaeda.
Aside from 9/11 none of them have operated successfully in the US and your domestic terrorism has mainly been perpetrated by individuals or very small one off groups of just 2 or 3.
It's worth noting the Weather Underground were well organized and sophisticated terrorists, although they were admittedly a lot less violent and long-lasting than the listed groups.
There was actually a fair amount of domestic terrorism in the 60’s and 70’s that doesn’t get widely discussed for some reason. FALN was another fairly successful domestic terror group that has gone largely forgotten.
Aside from 9/11 none of them have operated successfully in the US and your domestic terrorism has mainly been perpetrated by individuals or very small one off groups of just 2 or 3.