Because, most of the time, performance doesn't matter enough to justify it. Custom solutions are only necessary if you know performance is critical to your app

Because, most of the time, performance doesn't matter enough to justify it. Custom solutions are only necessary if you know performance is critical to your application's purpose, and that you need to squeeze as much out as possible. If that isn't the case, then you don't need to worry about the implementation details, because, in general, any performance changes won't matter.