Only for the most high level and serious cases would a technique like that be used, like counter terrorism, or high level drug traffickers, maybe. Like top ranking Sinaloa cartel members, maybe. Even, then the process to secure a surveillance intercept like that is so intensive. It's a high legal standard to even get a title III wiretap warrant, which is what they used here, I believe. You have to submit an affidavit, and resubmit every 30 days for every phone you want to intercept. They have filters for non related conversations, it's a whole ordeal. It isn't easy or cheap.
They don't just listen to part time dealers talk about their love lives or football for 5 months to get them on a quarter ounce deal. But, you see people acting like that all the time. "Oh you never know"