I honestly find it easier to build UI elements from the ground up over using plug-ins, because like with any other code if you are the one who developed it you understand it.
I too have been turned off by lightbox and slider plugins for jQuery, and find it easier to just come up with that kind of thing myself rather than jump into someone else's codebase.
I'm sure you have better things to do than build a lightbox from scratch. Take 10 minutes to learn someone else's solution and you can move on to solving the actual problem for which you were tasked, which likely has little to do with lightboxes.
Maybe, I mean I still use jQuery and any else that's relevant but a lightbox is such an aesthetic, simple thing that I wouldn't consider it NIH to prefer creating one that suits a website more (if the website's design is a big focus)
I too have been turned off by lightbox and slider plugins for jQuery, and find it easier to just come up with that kind of thing myself rather than jump into someone else's codebase.