This isn't necessarily about Gimp, but this is a general problem with software developers creating tools for their domain.
It is easy to create a tool that is specifically tailored to your workflow, because for parts that may tough to code, you manually take care of it. It becomes harder to generalize that tool for public use. It is harder still to add good UX that lets novices pick it up and begin working.
It seems easy, because the ubiquitous tools, libraries and frameworks have years of planning and experience to learn from.
It is easy to create a tool that is specifically tailored to your workflow, because for parts that may tough to code, you manually take care of it. It becomes harder to generalize that tool for public use. It is harder still to add good UX that lets novices pick it up and begin working.
It seems easy, because the ubiquitous tools, libraries and frameworks have years of planning and experience to learn from.