if you can tap on petabytes/s of data with your probe, how can you move that data for analysis or how can you decrypt it in real time in case you only want to retransmit portions of it?
You should read the Snowden papers (or was this some other leak? I’m getting so confused by all the leaking). They have two methods: first a device at the location dumps most of the traffic they don’t need like porn or torrents. The remaining data can be reencoded to look like normal https or ssh or whatever and sent through a third cable to another main network location. The data can also be stored locally and retrieved.