I think the journaling is more about getting it off your mind so you can let the feelings go, at least a bit? I don’t think it’s going to work for everyone, nothing else does lol, but that’s the idea behind it. Catharcism. It’s the same as writing letters you never intend to send to whoever you’re writing to.
I know if I’m angry when I write my diary, I allow myself to feel it while I’m writing, so the writing itself is my emotional release. When I stop writing I feel more able to let the feeling go, because I’ve processed it, at least to a degree.