The sheer volume of communication data is far too large to monitor everything.
By people, sure. Run it through a magical analytical algorithm that flags stuff for people to look? Or if that's still too much everywhere, they could focus it on a certain area's towers and process that data. Will it catch everything or not generate false positives? No, it's not perfect, but I could see it helping them and being done.
I doubt an agency like this would just hoard the info and not proactively use.