I don’t think this is true. They might struggle with distractions elsewhere but if they’ve created a ritual out of writing in this distraction free environment they’ve created it will probably always work for them (and maybe better over time). Having the experience of doing things without distraction might also help them ignore distractions elsewhere.

By way of analogy, learning to swim in calm waters helps you learn to swim in rough waters by giving you the experience of what swimming is even like.