The important thing in any "large" application is to set consistent patterns for doing common tasks: creating UI components, re-using them, updating their content as a result of data changes (reactivity), etc. This can be done with or without a framework.
A framework establishes a large portion of those patterns upfront. If the framework is a popular one (e.g. React) rather than an in-house one, it makes it easier to quickly ramp up hires and have a lot of documentation/examples online. Popular frameworks also implicitly contain a lot of knowledge from years of feedback from thousands of devs exercising its APIs and providing feedback, so they're typically pretty good at solving common use cases.
Obsidian was initially built by a single developer. One of the best that I have the pleasure of knowing, but when you're one person, it's much easier to create your own pattern and have it work for yourself. They have since hired maybe 2 other devs, with minimal intention of hiring more, so ease of onboarding isn't a significant concern to them the way it would be for most companies (and "large" frontend apps more often than not require larger teams, by definition).
Thank you for your comment (and replies). This makes me realize that we can also actively choose which patterns of a framework we want to use, and which aspects of a project are better built to work independently.
Also, so cool that you got to know Silver! Their team is small but very talented, I look up to them a lot.
A framework establishes a large portion of those patterns upfront. If the framework is a popular one (e.g. React) rather than an in-house one, it makes it easier to quickly ramp up hires and have a lot of documentation/examples online. Popular frameworks also implicitly contain a lot of knowledge from years of feedback from thousands of devs exercising its APIs and providing feedback, so they're typically pretty good at solving common use cases.
Obsidian was initially built by a single developer. One of the best that I have the pleasure of knowing, but when you're one person, it's much easier to create your own pattern and have it work for yourself. They have since hired maybe 2 other devs, with minimal intention of hiring more, so ease of onboarding isn't a significant concern to them the way it would be for most companies (and "large" frontend apps more often than not require larger teams, by definition).