As someone who wants to try his code, this is easy to say. But more often than not, hacks and imperfections in the code will be pointed to and laughed at. Companies interviewing him might think less of him, etc. They will get angry with him if he doesn’t fix bugs they find. And do we really expect the community to be appreciative of what he’s done? Open source developers talk about how they maybe make $100 in donations for libraries that millions of people use.
It’s easy to tell someone to share something without understanding there’s usually more harm than good.
I think I write decent code. But I haven't always. And I've at least always tried to put everything I can up on my public GitHub, and even when my employer has been cool with it, just tossing generic non-competitive code (not core to the business) up on GitHub as well. My experience has been the opposite of what you say. I've never had a single person mock me, I've only ever really learned things from comments/issues, gotten value add from PRs, or been encouraged to see that people like/use my code. It's been one of the single greatest sources of learning in my career.
Quite honestly, the employers who are out there that would look at code I've put out there, see a bug, and pass up my resume, are the kind of employers I would almost certainly be just wasting time with if I was to work there. So in that sense it probably only does me good too; I get to spend my time at companies that understand the journey, understand differences of opinion and design, and don't expect perfect code that 100% matches their style guide every time.
The reason I write code is not at all exclusively to make money. And the code I use daily is free and open source by probably a factor of 10:1. So I like to give back where I can. I'm not looking to make a buck, but I'm also obviously gonna put my GitHub on my resume because I'd much rather be matched to employers who can observe my approach and appreciate it enough to bring me to the interview stage.
It’s easy to tell someone to share something without understanding there’s usually more harm than good.