My quick skim of Wikipedia may not be telling the complete story, but it says the initial release was 9 years ago (February 2016). After nearly a decade, I would hope that things would be out of "extreme beta mode," but I guess this isn't the case?
In 2018, seven years ago, Andrew announced he'd go full-time on Zig and quit his paying job to live off donations instead.
In 2020, so five years ago, Zig's 501(c)3 the ZSF was announced, to create a formal structure to hire more people in addition to the few already on Zig.
So, "most of its time" is just not true. For "most of its time" Zig was a small, largely independently funded project for multiple people, for a tiny period it was a part-time project, and for a while after that it was solo, but those weren't the majority of its existence.
I like to compare this to real world cathedral building. There are some cathedrals that are literally taking centuries to build! It's OK if the important, but difficult thing takes a long time to build.
If you keep up the development pace you're going to approach stability. Unless you're in a manic spiral of rewrites.
Making a programming language from scratch is a long endeavor when it's a one man project.