"Bomb factories" are where they found assembled bombs and the materials for making them. "Weapons caches" are where they found large stores of weapons including heavy-duty military ones that were specifically outlawed by the agreements the Palestinians signed. Slightly more than circumstantial evidence.

And these bombs are manufactured by professional demolition people, who know exactly what they are doing. I have noticed that recent bombings seem to involve less-sophisticated techniques. The last suicide bomber used a suitcase, which takes less skill in assembly, and other attackers just threw grenades.

It's possible that the "pros" have been either killed or captured, making the "bomb belts" harder to come by.