You'd struggle to extract a maintainable codebase from a C# or Golang web server after the fact too. As an industry we've been making simple websites on shared hosting for over a generation, clients who ignore the entire world of information about the dangers and pitfalls on this topic are squarely to blame as negligent. It ranks up there with not paying taxes and then acting shocked when the government comes knocking.

While Javascript could potentially be contractually mandated to be written in a way to facilitate production codebase recovery, if you knew enough to ask for that you wouldn't, you'd require them to use your source control and to provide build/deployment scripts instead.