Digital context is important for attention
Context shapes a lot of what we want to do in any given moment. For example, I’ve been playing a lot of games at my desk lately. When I sit down at my desk, my mind immediately goes to gaming.
In the same way, your digital context matters for your attention. If I use a notetaking app like Obsidian primarily for writing music, I will think of music over my Zettelkasten whenever I open the app.
This, to me, is the best argument to use different apps for different purposes. When I open Obsidian, I want to solely think about my research, study, and writing, not about my to-do list or my upcoming applications.
There is, of course, the problem of categorization in siloed apps.