You don't use tags for searching for answers. You use tags to browse questions on topics you know a lot about and you have a high chance of being able to answer. Most of the questions on stack overflow I know nothing about so I browse the ruby tag where a lot of the questions are in the range of what I could answer.
Thats why they have the requirement for a tag "Could someone be an expert in this tag?"
Thats why they have the requirement for a tag "Could someone be an expert in this tag?"