Web Browsers have a sort of inner platform tendency where they roll their own window management, and it just gets very messy and integrates incredibly poorly with the window management of the operating system.
You can open CI in your browser to see how your build is progressing, and in the same window, with a few keypresses, check your private email and then go buy new tires for your car, file your taxes, and after that go watch some porn.
Web browsers are streamlining an undesirable type of context switching: These are all tasks from separate domains, and I don't understand why it would be desirable that all of these things are easily accessible from the same window at the same time.
Having dedicated launchers opening specialized windows allows for a sort of workspace mise-en-place that makes interacting with the computer much more focused and deliberate. Each tool has its place and function.