The author has written their own HTTP server rather than using the one provided with the JDK. They need to have a really, really good reason to do this, and i haven't seen such a reason reason documented anywhere.
Other, much larger, web frameworks provide their own HTTP servers (or bundle Jetty etc), because they can make them more scalable, or more featureful, or support protocols the JDK one doesn't. But i don't think the author's HTTP server does that.
> You will be hard-pressed to find another modern project as obsessively minimalistic. ... This follows self-imposed constraints, predicated on a belief that smaller and lighter is long-term better.
the reason: obsession and self-imposed constraints.
Other, much larger, web frameworks provide their own HTTP servers (or bundle Jetty etc), because they can make them more scalable, or more featureful, or support protocols the JDK one doesn't. But i don't think the author's HTTP server does that.