It depends on the browser.
Flash Player is a built-in component of Google Chrome and Internet Explorer on Windows 8 and higher. Neither requires a separate download or update.
For other browsers, building, maintaining and distributing Flash Player to 1.2 billion users is a tremendously expensive undertaking for a product that we offer free of charge. We provide bundled offers with the downloads as a cost-recovery mechanism, which adds some friction to the installation process.