For semantic reasons.

Each element in HTML should correspond to a proper semantic element. For example, navigation elements should go within <nav>. Elements like <center> are remanants of the good ol days when css wasn’t mature enough and you’d add color to an element via attributes. Obviously, center has no semantic meaning and pretty much useless in web dev now. It hasn’t been removed but deprecated.

These are "should"s and not "must"s. This is why divs exist because many times it’s hard to decide what semantic meaning a piece of content has, so divs are just generic components when you can’t think of an better semantic tag.</center></nav>