Besides the obvious reason why MoviePass would not buy tickets for the first two weeks of a "tentpole" release, there is another reason why.
First, the obvious reason: "everyone" wants to go the first week. (The second week is usually 50% - 60% of the first week). If you assume that nothing changes (there's obvious limits to this assumption, but lets just roll with it…), MoviePass pays for 50% fewer tickets. After week 2, that's 25%. (Remember, the "each movie once" limit problem remains as well).
So, some might think that the non-obvious reason is that MoviePass might be able to buy discount passes. But that isn't the real reason. Why are passes cheaper? Because of "the split".
So, if MoviePass wants to focus on the "exhibitors" in its dealmaking, it needs to focus on driving revenue in their hands. Paying for the tickets that pay them more is the obvious extension of that focus that nobody seemed to catch (in what I read or watched).