Churning only sometimes works. This thread explains some of the reasons why: https://www.reddit.com/r/Monero/comments/oz69hf/churning_why_is_too_much_detrimental_to_privacy/

One that I'd like to highlight is that Chainalysis tracing video shows a bunch of monero transactions where they managed to eliminate all of the decoys and identify the true spend. Churning makes another transaction where they have to do that in order to see where it goes next, which probably helps since they can't always eliminate all decoys (I don't even think they can *usually* do it), but your mileage may vary.