I think it's fair to say there is a large contingent of 'deterministic' players out there. My evidence is a poll taken in EU3 where people were asked if they played a mod, and if so which.
Vanilla did indeed win. Barely. MM came in a very close second IIRC.
MM is not as deterministic as say EU2 was, but it certainly has its moments. IIRC Muscovy WILL inherit Novgorod, Austria WILL 'diplo'annex some of their historical lands and so forth. The Knights of Rhodes WILL find a new home if you take Rhodes/Malta/the Crab Nebula from them and event-attack Muslim states where they have the opportunity to DoW them. I might have some of the fine details wrong as I haven't been able to do much with MM, but that's the gist.
Vanilla does indeed need to stay sandbox mode. First off, it's very popular. Second, it's the necessary building block that mods will use to make a more historical/deterministic variant. I think if a Russian/Ottoman/etc. player wants to trigger something to the Crimean War it'll be possible....without being forced. Similarly a suitably militant Paraguay probably WOULD alarm its neighbors and start a war - while a more passive one wouldn't.
When EU3 came out, I was worried where this sandbox world would lead us, but now I agree with previous posters. Decisions and event chains help lead the game onto plausible, if not necessarily strictly historical paths. Missions can also help guide you. A little imagination fills in the gaps. As for logic, God knows we players make errors, and the AI can be counted on to do something bizarre. Just like IRL politics.
A LOT can happen in an EU or Vic timeframe, and playing EU2 I definitely ran into moments where an event was nudging me back into a historical path long after it made sense. (My experience with Vic1 was unfortunately short and painful. I'm hoping Vic2 is gentler to me.

) Whether sandbox makes sense in a very short time frame like HOI3 could be a fair question, but not germane to this discussion.
Incidentally EU1, which started this whole ball rolling in the first place, is almost completely sandbox....