There's probably quite a few people who couldn't play during the week. There were hudnreds of thousands copies sold in the last few days, not everyone could play right away. I got lucky and managed to squeeze maybe 10 hours in...

There also might be people who bought it from Steam, since the word got out it's better for Wube, but then went to factorio.com and got a copy unconnected from Steam. But yes, even before, there was a surprising number of people who didn't get any achievement ever.