Showing that you tinker and explore outside of your day job is attractive to potential employers. The fact that the code isn't amazingly architected is not a negative.
> I have yet to see a job I'd be otherwise qualified for or interested in list "have a github profile with projects for us to look at" as a requirement, or even a nice-to-have.
Every job on this job board has such a requirement.
at least for web development it seems almost mandatory.
That may be true, but there's a whole world of programming jobs out there that have nothing to do with "web development". There's all sorts of internal corporate app stuff, embedded system/firmware, control systems / automation of various sorts, scientific computing, simulation software, data mining / machine learning stuff, etc., etc., etc.
> I have yet to see a job I'd be otherwise qualified for or interested in list "have a github profile with projects for us to look at" as a requirement, or even a nice-to-have.
Every job on this job board has such a requirement.