Once you start digging into productivity tools, it's easy to fall into the urge to use an all-in-one tool. Doing absolutely everything inside Notion or Obsidian, for example. You also start stringing integrations between apps all over the place.
People who are drawn to this stuff care a lot about efficiency, and using a single tool looks more efficient than using several, which I think is where the tendency comes from. But the all-in-one tool is a trap. It fails to account for the mood of using a specialized tool.
Have you ever seen a craftsman use only one tool? If anything, you might use an all-rounder tool as a beginner, but the more skilled you get, the more you reach for the tool that fits each situation. The same goes for knowledge work: as your proficiency rises, the number of tools you use grows. That's partly because of each tool's special capabilities, and partly because each one feels different to use. When I'm in Obsidian, in Calendar, in Reminders, in Jira, in Confluence — every one of them carries its own distinct feel as I work.
And this is my own bias, but I've never once seen a tool that bills itself as all-in-one actually do several things well. Everything is there, but every one of those features is missing a screw somewhere. That's because any company has limited manpower for building its tool, and limited resources can't satisfy every requirement. So software that claims to be all-in-one is very likely to be a half-baked product.