This might be worst in the news industry, but it is not uncommon on other sites too. And even without a tag manager, as a web developer, I still get requests to blindly add all sorts of scripts. Often they're requested by a marketing partner of the client, or because the client has seen something at a conference that they believe they must have.

Wherever possible, I make it clear that this cruft comes at a cost, but I cannot recall a single client being swayed by those arguments. In the case of overlap between trackers (Analytics, Facebook, etc), from the perspective of the client, they solve their "problem" in a quick request. Either it appeases the marketing company or it gives them that little extra feature they think they need but will never use.

Increasingly, it can be miserable developing for anything other than my own projects because of how much time is spent implementing bad ideas requested by other people.