I've seen multiple examples of "enterpisey" web apps, and there was no joy, just because developers didn't know how to build a good application with JavaScript and even more - they didn't care at all.

With a "don't touch anything that works" mindset that lots of enterprise developers have - you write write-only JavaScript code and when it becomes too large - of course, there is no joy in touching this kind of codebase.

Every enterprise project with a in-browser front-end needs a good front-end developer from the start to set up good code, good practices and good attitude to a front-end part of the code, and it will be fine: the joy won't fade away.