I think it's the first. The guys played the first however many games of the year without Zion, and they don't know how to play with him, and in close games I think they decide (possibly subconciously) that they'd rather stick with what they know than try something new. The consequence is that someone like Jrue or Ingram ends up taking shot after shot, missing all of them, while Zion battles for position in the paint, or cuts down the baseline, and gets resoundingly ignored.
Maybe there is some selfishness, maybe there is some heroball going on, where someone who has been the closer for most of the season (Ingram, in this case) says to themselves ''hey... this is my team. I'm the all-star here, I've been called upon to close these games, why would I give these shots up to this rookie when it's my job to win this for us?'' but I don't get that vibe from Ingram. Maybe he is actually thinking that, idk, but I think it's more likely a subconscious decision where he just makes that choice without even realising it. Same for Jrue, same for Lonzo.