1) Choosing to split up tools in this way is a valid form of self control called precommitment. https://en.wikipedia.org/wiki/Precommitment

2) Apps may change and often experience “enshittification.” Hardware can break but non-connected hardware is otherwise unlikely to change.

3) Many apps collect private data through telemetry or ad networks. Data may leak or be sold.

4) Decoupling allows you to precommit to different situations. For example, you could bring your media player but not your phone to your workout if you have trouble staying on task, or if you just want to disconnect for a while.

5) Many people have limits to their self control, hence the prevalence of destructive addictions (gambling, alcohol, drugs) in society. For these people it’s a good idea to precommit when possible in addition to working on other skills to manage the problem.