It may seem simpler to integrate one of the thousands of PHP login scripts that show up in a Google search - and perhaps it would be, at first! But over time, a purely procedural approach tends to leave you with a big ball of mud - a project that is poorly structured and nearly impossible to maintain.
Furthermore, many of these "user scripts" tend to lack proper maintenance and long-term community support. Bugs and other issues in their codebase can easily end up being your problem, and you may end up needing to significantly rewrite these scripts when major design and security issues come up.
UserFrosting does take a little more work to set up and learn at first, but it's worth it and we're here to help. The concepts and design principles you'll learn as you write (or rewrite) your project with UserFrosting go far beyond this framework, and even PHP itself! You'll come out a stronger software developer with a more robust application - how many other login scripts can say that?