I really don't see the point of using cars (parts are fine). You should build your own. It's a lot easier than you think and you get full understand and control of your vehicle. Learning and mastering someone else's vehicle usually takes longer and it may not solve your specific transportation needs all the time.

Besides it being flat-out wrong that mastering a framework takes longer than building one (you will have to support it), the typical framework is a lot larger than the code of the applications built on top of them.

Building a framework is a bit like writing a DSL, a good framework abstracts out the work that would otherwise be duplicated many times over and will help to standardise the codebases of various projects and will help to allow integration of bits and pieces from different projects in a re-usable way.

There is a reason why rails, django, drupal and a bunch of others are wildly popular, they save people oodles of time.