For example, I have posted quite a few questions regarding mathematics in general, because I want to learn more about the field and I just want to make sure I get an answer or an opinion from someone who has good knowledge about my question. I tag it with the advice tag and I have seen, more than once, that people want to close it or it gets downvoted. It's not like it's a bad question but people don't want it on the mathSE website. So if that's the case and that's how people are going to be, what's the point of the advice tag if people just want to close down the question? And I have also noticed that it's not just my questions, but others as well.
There are currently 106 (not deleted) questions tagged with the «advice» tag, and only a few of them are closed: exactly 12.
There is the possibility that your questions are being closed for reasons other than the tag!
Moreover, as far as I can tell, none of your three advice questions is closed (although you have an extra one which is deleted)
I think the problem is one of the kind of advice being sought. From the FAQ:
"You should only ask practical, answerable questions based on actual problems that you face."
All questions asked on the main site should be definitively answerable, in the sense that they should not be open to interpretation, where different opinions may be equally valid. I think that most "advice" questions that get closed are closed because they fail to meet this criteria.
An example of an advice question that might be closed is "What is your favourite method of studying linear algebra?" Whereas the similar question "What are some good books to learn linear algebra from?" would probably not be closed.