I think the main reason is because of how Tag Badges work (see the Tag Badge section in the link). Tag Badges only count how many non-wiki answers you post, and how many votes you earn on those answers. It is also how this tab sorts your tags (by total number of up votes minus down votes on your answers for the badge).
As for why questions don't count, well, tag badges are to show how knowledgeable you are for that tag. Asking questions doesn't really represent your knowledge on a topic (in fact, you could argue it shows the opposite - no offense intended, it's why the site exists)!
If you hover over the number to the left of the tag, a tool tip will show up with some information. This below screenshot is for your minecraft tag:
Note that the number to the right of the tag is the total number of posts (both questions and answers), so if you want to know how many answers you have per tag, you will have to hover over the left number and read the tooltip (or if the tag is trackable, you can see your progress through there).