Imagine a software company with a 50M LOC codebase that shuts down and lays off all workers. The office is still there, servers are still running, and nothing has been touched--but the employees are all gone.

How easily do you think a new team of the same size could come in and restart operations? Most likely it would take a long time and a lot of capital before that company was productive again.

That's what the parent means by social infrastructure: institutional knowledge--all the stuff that isn't written down anywhere.