They've tried that approach but it's actually less efficient than "good old fashioned police work" because it turns out that 99/100 of your hits are gonna be lawful weirdos, 1/100 is gonna be a petty drug dealer and the career advancing prosecution you actually wanted would have been much easier to find by using normal methods like inferring that a dealer has a supplier, a spy has a handler, etc, etc and trying to suss out who those people are. The NSA figured all this out post 9/11 when they were building data haystacks in search of terrorists.
What the data haystacks do get used for is dragnet policing wherein an agency picks some crime they're gonna go hard on, pulls up a bunch of results of people who probably did it, tosses all the people who are likely to pose any risk to them (e.g. you don't see the ATF knocking on doors asking about Temu glock switches in bad parts of Detroit) and kicks in the doors of whoever's left.
The data haystacks are also really useful for witch hunts when they get egg on their face and need to make someone pay, like that time they prosecuted anyone and everyone who they could construe as having done anything to help the kid who bombed the Boston Marathon, and the January 6 people of whom a great number were certainly just hapless.
And this is in addition to the usual "opposition research" like the FBI bugging MLK and all that sort of crap.