There are a few things to say here. First off, the StackExchange 'back end' works in the same way for all sites, which means that 'we' (TeX-SX) have to use the structures as decided on by the 'Powers'. Occasionally that means we have some oddities. That leads to the second point: 'off topic' is (currently) intended not only to cover questions which are out-and-out not about TeX, etc., but also for things that are not answered 'by convention' (I'll return to this below). The latter has tended to include stuff like typos, mistakes reading the docs and so on. The logic there is that the StackExchange 'concept' is that it's not a forum in the sense that the same question shouldn't be answered over-and-over and answers shouldn't be so focussed on the OP that they will never be of use to anyone else. Things like typos, needing to update a TeX system or misunderstandings tend to fall into this category: the specific question is not likely to get asked again, and any answer would probably not help another user.
All that said, probably the biggest reason here is that we don't have what we used to have: a close reason that is focussed specifically on a question being too narrow. The 'Powers' got rid of 'Too Localized' as they felt that it was being misused (across the network): the StackExchange intention for this was it applied to only things that could never be seen by anyone other than the OP, rather than being used for the type of case I've outlined (typos for example can come up on a lot of sites, and most don't answer them). The Powers have been very definite that such closings are because the question is 'off topic' (perhaps 'out of scope').
I think it's fair to say that many of us feel that closing these 'localized' questions is the right approach ('read the manual' is not really adding value) but would prefer a better reason than 'off topic'. However, at present we don't have one.
Note that in some cases the best approach with 'good' basic questions is to sort out a canonical answer and then dupe to it. Probably the most obvious example is Question mark or bold citation key instead of citation number, which is a good question with a good answer to a very common issue.