I don't really know, but my guess is that silkscreens are cheap and make manufacturing a lot easier. In particular, if the board isn't labeled, they won't know

I don't really know, but my guess is that silkscreens are cheap and make manufacturing a lot easier. In particular, if the board isn't labeled, they won't know if is the right board and the right version. (Even for the boards I make, it's hard to keep track of the old version versus the new version if I don't put a number.) You could label it in the copper layer, but that's harder to read. A silkscreen will make manufacturing a lot easier since you can see what goes where. QA would also be a lot easier.