For many of us, the way we manage software projects has changed has changed so much since the days when Joel wrote this.
It was a different age, with different products. I’m sure there are still products built the old ways, but Joel was writing before SaaS and CI/CD and endless roadmaps.
Reading into Joel, he was building SaaS. Fogbugz to name one.
He seems to have other posts on the lifecycle of software and product budding. Maybe it wasn’t mainstream then but some folks were doing meaningful parts of it.