Without knowing more details and examples about questions you are talking about it is impossible to answer this objectively. Questions might get closed incorrectly, though it is subjective to define 'incorrect'. There are well defined guidelines for closing, but they are subjective to each user's interpretation. So we should always trust community's judgement together with using the system's tools (such as reopening votes and discussions in meta) to correct misjudged calls.
Now, answering more broadly:
Why some users close many questions as too-broad or unclear?
Why some users do not? My opinion is that we could be doing more.
It is important to remember that the main objective of most Stack Exchange sites (including GIS SE) is to build a repository of high quality content regarding on topic subjects in our community. This is important because questions which are not well posed (on-topic, well written, relevant scope) have greater chances of being downvoted; closed as off-topic, unclear, broad or opinion-based; or abandoned by not getting any attention and consequently automatically deleted by the community bot). By doing so, we are already helping users to quickly find good answers to their questions.
If we don't do that (keep a high signal-to-noise; or at least try), it is going to be increasingly difficult to find good stuff here, users will eventually quit contributing, and GIS will resume to other existing forums where we search, search and end up frustrated by not finding (or taking too long to find) useful answers.
Is there a Mafia or something here?
Depends on the POV (a mafia of volunteers trying to curate this site?).
I feel bad when newcomers get their questions closed (my first in SE was), but the system also has plenty of mechanisms to help turning around (one of them is that if the question is edited within a five day window after being 'put on hold', it automatically goes to the reopen queue where it will be re-assessed for reopening; what we can't to do though is to edit 'on hold' questions with irrelevant edits). Additionally, a new tool coming is the question wizard, which I believe will help a lot.
Moreover, every time a question gets closed, there will be plenty of messages explaining what to do next, links and comments from reviewers pointing to our tour page, help center page, posts on Meta, etc.
