I've heard of this before as "Not invented here" syndrome. Frameworks are powerful as they give all developers a common language and methodology for doing repeatable tasks, meaning that when I need to fix a bug in your code, I know how it is architected and where the code should be because you have used a framework I understand.

Not to mention that these frameworks undergo alot more extensive testing than an average developers code will ever go through. By using a framework you benefit from not having to go through the pain of dealing with all the different browser models and quirks that every version introduces or takes away.

For really advanced or incredibly high performance tasks you might be correct but to me that is the 1% of tasks, for everything else a framework should give you all the scaffolding you need allowing you to instead focus on tasks that add real value into the product/service you are working on.