It's all about the social impact of a mistake.
The reason "engineers" sign off stuff is not because they are engineers. It's because society frowns upon people dying due to a faulty building, wants to see those responsible for the disaster punished and not be behind another project again.
Society's response to ensuring incompetent professionals can't sign off on stuff is to manage an Allowlist of individuals who can sign off, and have mechanisms in place to remove from the Allowlist those who screwed up badly.
These Allowlist are things like professional engineering institutions, and someone who is registered in the Allowlist is called engineer.
Now, does the software engineering world have anything of the sort in terms of importance in a society? No. A service crashing or a bug being sneaked into a codebase does not motivate a strong response from society demanding some people do not ever get behind a keyboard again.