I estimate the vast majority of "web projects" begin with npm installing something of some sort, yes. React is dominating the web development space (judging from the average "popular web stack 2025" search result), and it and a significant portion of the competing platforms start with installing some dependencies with npm (or yarn, or what have you). Especially projects that compete in the same space as Lit.

That isn't a criticism of projects that don't use npm, and it doesn't make them less valid, but it makes sense for the documentation to match the average developer's experience.