Moderation is done by the users of a stack exchange, it's a set of privileges you earn as you gain certain levels of reputation, it works the same way on stack overflow.
The people who closed that question as off topic weren't moderators, and elected moderators mainly deal with harassment, spam, and edge cases. Moderators have the diamond next to their names, and have to be nominated and win votes from the sites users in an election, they aren't appointed.
I'm quite sad of all this being so rigid. Here In Italy we have a word about this kind of behaviour, and it has been learned through history.
We have a scope, and we stick to it. Changing it has been proposed a few times, but fundamentally there are several problems that haven't been solved:
- developers who would punt their users here to save money on support (this already happens, and violates the TOS of Stack Exchange)
- questions about premium plugins that need people to pay to even see what the problem might be that stay unanswered
- users trying to get free dev support for premium themes and plugins without paying
In every case, contacting the original authors gives far better results. When a 3rd party plugin refuses to offer support, be it paid or unpaid, Stack Exchange rarely has the people with the experience the authors had to answer a question.
Case in point, WooCommerce questions rarely get answered here.
But lets take the question used as an example:
I'm using WP All Import and Polylang to import more than 500 products. However I cannot link products uploaded from my csv/xlsx file. The structure of file looks like this:
This site is for WordPress development, but this question immediatley states that it's a WP All Import + PolyLang question. Not only is specialist knowledge of WP All Import needed, but specialist knowledge of both PolyLang, and the combination of the two.
The chances of those kinds of questions being thoroughly answered is rare and unusual. The site simply isn't the appropriate place for it to be asked. That doesn't mean it's not a good question, just that this isn't the place for it.
As for the other rules, they were mostly derived from stack overflows rules. E.g. plugin recommendations are off-topic because they're "shopping" questions, and the same is true on stack overflow and the majority of stacks ( the software recommendations stack being the notable exception )