Why tags are displayed bellow the content and not inside

So if I look closely, seems our actual question is “Why does WordPress put Post Tags at the bottom of a Post?”

The answer depends on the theme, of course. But, most themes put them after a post’s body so that you can use it as part of browsing away from that post, to get involved with further reading. Basically like saying, “You’ve been reading about: Toys, Babies, Books” where each of those items is a link to, presumably, articles on those topics.

The idea of having them at the end of the article is so you don’t get bored too quickly and jump off to read something else.

Unless you mean something else by tags as that can be a pretty vague thing around these parts.