I also struggled when I was trying to build the habit on journalling: the first month was easy riding in high motivation. I thought maybe because I didn't make it "atomic" enough. It clicked for me when I realised that voice journalling was more suitable for me, in contrast to pen/paper and even typing.

I even made a while service around that in case others find value in it (link in bio)

I think the author just didn't break down his habit into small, inexcusable steps