I think a few reasons. One being that this team is functioning at about 60% of what I believe our full capacity is. It's a transition period, and being able to fall back on 'just being yourself' or 'just being natural' is hard because we don't even know what that is, so it leaves us overthinking things, and we're overthinking the past two games and haven't had enough bunny games to get in a groove. Other variables include Embiid coming back, plus 48 minutes of Embiid and Horford being able to drag Gobert out of the paint, unless Gobert is guarding Simmons. If he's pulled out of the paint for their shots, or if he contests a shot, you'll have one of Embiid or Horford available to fight with the rest of our poor rebounding guys.
I believe we can beat Philly, but that's when we're actually established. Until then, it's a crapshoot. I'm not saying for sure we lose, and I'm not saying we suck if we can't beat them, but just saying that my head would lean a bit more to this being a loss.