Because of injuries, mate.
Ok, very unpopular opinion incoming:
Romero, VDV and Vicario are essentially the three starting players we are missing. Forster has done a great job coming in for Vic. Are we really that reliant on VDV and Romero (who has been accused of falling asleep countless times this season) to perform well as a team? Are they all we need to get this train back on track? Really? Sure, we miss players in certain positions, but none of them (bar Bentancur, who hasn't had a great season, tbh) have featured much anyway. We barely use Bergvall, Moore has gotten minutes here and there, Gray has played all over the place, bless him, Spence couldn't get a start if his life depended on it.
It obviously sucks that we now have to use Gray and Dragu in central defense and have knackered players (lack of rotation could explain this bit), but is it really that much of a mitigating factor for the performances we've seen as of late? Really? Or do we just have a poor squad?
Maybe so! What do I know. Maybe so. With a fully fit squad we would obviously be better, but we're never going to have that (especially with how we train, even Ange has admitted as much), practically no team ever have a squad fully fit.
Again, as I've said many times - I hope we and Ange manage to turn this around, I really do, we play exciting football when we're good - we just need to be good more consistently, and certainly not bad as consistently as we have been lately.