They know that one big arrest will set the cards to tumbling on their house of corruption and expose them all. That would lead to them taking measures we don't want to happen. Slow and deliberate steps to eliminate their structures of power and control, from bottom to top, is the only way to assure that doesn't happen. This is why Trump had to let them go as far as to call on Antifa/BLM to act out. It was in their playbook. He knew they had to be cleaned up first, and the only way to identify them all (and collect evidence on their funders/supporters) was to let them act out so he could track their network.  There are still other threats we haven't seen, only because Trump has been very careful not to alert them with major arrests. Bottom to top keeps them complacent while their power structure is disabled. They could call on China to start WWIII. They could call on the world banks to cause severe economic problems. I'm sure I'm overlooking a few other possible threats.