The fact that Uncharted: Legacy of Thieves Collection now looks to be Sony's weakest PC release to date could, of course, have many explanations. For one thing, they're actually five to six-year-old-games at a relatively high price tag, and it's probably not a wild guess to think that many people probably already had time to play them on PlayStation 4. The PC release also coincided with Gotham Knights, A Plague Tale: Requiem and the Call of Duty: Modern Warfare II campaign, three brand new and massive games that have obviously attracted a lot of people.
In fact, looking at the numbers, Nathan Drake's collection underperforms badly when compared to other Sony titles released on PC after a period of console exclusivity. A paltry 10,851 were sold during the release weekend, which isn't even enough to earn a spot on the Steam Top 100. That's compared to Days Gone, Horizon Zero Dawn, Spider-Man and God of War, which had anywhere from just under 30,000 to over 70,000 during their respective launch weekends. See the image below for more detailed figures.