If we compare like with like and assume that in both cases you're developing locally on windows and running on GH Pages, something established like Jekyll has a much better chance of working consistently on those different OSes than a hand-written script, IME.
Yeah, absolutely. But we're talking about optimizing for complexity ("do I understand this?") rather than compatibility/features/functionality/security/community support/any of the other things you get from using established frameworks.
I'm not defending the decision, but I have worked with several folks who have this approach to using their own tools — and at times I lean in this direction too, until I have encountered breakages more often than I care to "understand them" by using my own tools — and hence trying to dissect the motivations behind that choice.
