Tomb Raider sold much better on PS4 even with Spider-Man. No idea how you came to the conclusion that the last exlusivity deal killed it. XBO sales shouldn't be negatively impacted by it which means you believe that the new Tomb Raider would have sold like 4x more on PS4 as on XBO without the last exclusivity deal and that just doesn't make much sense.
It sold as much more on PS4 as you could expect with the difference of sold consoles and a huge release like Spider-Man. That game obviously took sales from Tomb Raider.
People just don't care much about the game. It doesn't feel like a game you need to play especially after the last two games. I really liked the first game of the reboot and absolutely don't care about the new one and I'm not the only one who thinks so.
It's not a FIFA which people buy again and again for new seasons.