Did you just ignore everything in my post to reply with this?
It's ok to not hit reply if you have no reply, breh. The post you're quoting literally says the term Superman isn't even uttered in Man of Steel, yet you want to ask me why Clark becomes Superman in Man of Steel? You were actually moving up the Marvel stan power rankings but this one knocked you down a few pegs
But I'm going to answer your question cause I'm intrigued if the replies can get even worse
In Man of Steel Clark becomes Superman because he chooses the existence of humanity over a second chance for Krypton. Humanity dubs him Superman.
He doesn't actually become Superman until Batman vs. Superman where he chooses to accept the burden of not just helping, but also being a symbol/hero and everything that comes with it.