The offices responsible for redactions are usually in-house legal shops (e.g., an Office of Chief Counsel inside an agency like CBP) and the agency’s FOIA office. They’re often doing redactions manually in Adobe, which is slow, tedious, and error-prone. Because the process is error prone, the federal government gets multiple layers of review, justified (as DOJ lawyers regularly tell courts) by the need to “protect the information of innocent U.S. citizens.”
But the “bad at redactions” part isn’t an accident. It functions as a litigation tactic. Makes production slow, make FOIA responses slow, and then point to that slow, manual process as the reason the timeline has to be slow. The government could easily buy the kind of redaction tools that most law firms have used for decades. Purpose built redaction tools speed the work up and reduce mistakes. But the government doesn't buy those tools because faster, cleaner production benefits the requester.
The downside for the government is that every so often a judge gets fed up and orders a normal timeline. Then agencies go into panic mode and initiate an “all hands on deck.” Then you end up with untrained, non-attorney staff doing rushed redactions by hand in Adobe. Some of them can barely use a mouse. That’s when you see the classic technical failures: someone draws a black rectangle that looks like a redaction, instead of applying a real redaction that actually removes the underlying text.