It seems like this is the central thrust of your question (emphasis mine):
I still see very good questions that are at the top of the upvotes list, but some of these other questions don't deserve to be up there. For people who may just come on here to find good questions, they'll come upon "less useful" questions. This defeats the whole purpose of SE.
If I understand you correctly, you feel like the top-voted questions on M&TV are just not very good questions. That's a valid viewpoint. I think what is happening is that your viewpoint doesn't match up with the majority of M&TV users. Further, I think there's a disagreement about interpreting the purpose of SE in general, and M&TV specifically.
For discussion purposes, we can refer to the list of M&TV questions, sorted by number of votes, highest-voted listed first, available here: https://movies.stackexchange.com/questions?sort=votes
On the first page of highest voted questions, we see a few specific movies represented: Groundhog Day, The Sixth Sense, Back to the Future (twice), Jurassic Park, Shutter Island, Fight Club, Pulp Fiction, and 2010.
Comparing that with the questions with the lowest vote score/most downvotes, it seems like you might have a point about favored movie "niches". None of the movies represented in the highest-voted questions appear on the page of lowest-voted questions. Also, Titanic appears more than once in the lowest-voted questions, and if there were movie snobbery going on at M&TV, a bias against Titanic questions seems at least plausible.
So on its face, your concern seems to hold water. Let's look more closely at the highest and lowest voted questions and see if the differences seem to be primarily about the movies in question, or whether other factors might be at play. First, let's review what the community has decided are the goals of SE and M&TV:
From the Stack Exchange Tour (emphasis mine):
We build libraries of high-quality questions and answers, focused on each community's area of expertise.
From the M&TV Help Center (emphasis mine):
If your question generally covers...
- Analysis of content or theme of all forms of Movies and TV series
- Identifying a Movie or TV series (see below for details)
- Questions about a Movie or TV show's production.
- The works of a director / an actor / a writer related to Movies & TV
The topics of the lowest voted questions include the following:
What is interesting about the lowest voted questions is that two of them are very similar to the question that started your chain of thought leading to this meta question. How long did Rose and Jack know each other for? and What “promise” does Coop make to Murph? seem to have been heavily downvoted because finding the answers was considered trivially simple to the downvoters (e.g., a simple Google search). That brings up the question: Are questions that can be easily answered not the best questions for Stack Exchange and/or Movies & TV?
According to this, there is no policy against "Google questions", and in fact, this states that "easy questions" are encouraged. Based on that, I feel a few of the lowest-voted questions on M&TV actually should not have been downvoted for the apparent or stated reason. Aside from that, the lowest-voted questions mainly seem to have problems not related to what movie the questions refers to. They do not seem to be about the preferred topics for M&TV, and some even fit into the category of questions that specifically should not be asked on M&TV.
Going back to the highest-voted questions, we see the following themes:
Referring to the Help Center notes quoted above, we can see that by-and-large, the highest voted questions on M&TV are right in line with the stated goals of the community.
So it seems hard to support the idea that certain movies are favored by "niches" on M&TV which is causing "bad" questions to be upvoted.
Moreover, it seems that the source of your dissatisfaction is most likely that you simply have a different opinion of what is a "good" question and what is a "bad" question than what has been agreed upon by the members of the M&TV and larger Stack Exchange communities. Most specifically: You seem to dislike "easy" or "Google" questions, while Stack Exchange policy favors such questions.
Point of agreement (edited):
This question: What has the greatest chance of being in Marcellus Wallace's briefcase? seems to me to be not a very good question on its own. It calls for complete speculation, the answer has been debated upwards and downwards across the whole internet, and it seems primed to create a meaningless argument. And yet it is one highest-voted questions on the site. Why is that? Is it because there are enough Tarantino or Pulp Fiction fans here who will just upvote any question about one or the other? Perhaps. It is true that there is no question on M&TV with the pulp-fiction tag with a score lower than 1.
That said, I think the most likely explanation for a question that could be considered bad or at least borderline having such a good score is what we might call the "great answer halo effect". The top voted answer contains a very informative, relevant, edifying, and amusing quote straight from one of the writers. Notice that the top voted answer has a higher score than the question. That is a good sign that the answer is deemed more valuable than the question. When there are good answers to bad questions, many voters are tempted (and I'm guilty of this myself) to upvote the question as well, since without the question being asked in the first place, there could not have been such a great answer posted. Also, this question is from 2011, when the site rules and criteria were likely different.
Should it be that way? Maybe, maybe not. I could see an argument in favor of upvoting questions that seem bad but accidentally provide great content for the site. A counter argument might be that upvoting bad questions with good answers encourages others to ask bad questions. Regardless, the way SE works is that the votes decide the score of a question or answer, and the voters decide the votes, and that's the system. So you have to take the downsides of the voting system with the upsides.