FISA 702 is not a criminal authority. It’s used in cases of foreign surveillance, cyber attacks, terrorism, and espionage. “Convictions” and “evidence” are not the right words, “intelligence” is.
The FBI is principally a national security and counterintelligence agency and secondarily a law enforcement agency.
702 is expressly for the counterintelligence and national security function, limited to foreign targets (non-US persons believed to be outside of the US), and if used properly will only incidentally and occasionally result in information related to persons practically able to be subjected to US law enforcement jurisdiction, whether or not they might in theory be committing US crimes.
Lots of indictments or other criminal process tied to 702 surveillance would actually be a sign of something unusual happening (of which “abuse of 702 for purposes at odds with its express terms” would be high on the list.)
It's about Intelligence, not Evidence. Intelligence (like anonymous tips) is what you use to find the Evidence, which is what you reference in the affidavit. Much Intelligence is speculative and/or bullshit and wastes everybody's time. Publishing Intelligence tips off associates of the adversary and betrays what you know and what your capabilities are, and possibly who you learned it from.
One would assume that a useless programs should be discontinued, simply because it’s not free to continue them.