FWIW, software engineers do have professional organizations like the IEEE and ACM, whether or not they back members in any significant way. There are also PE licenses although my understanding is that they are being discontinued for software engineering because basically no one was getting them in that field.

The thing that matters is not whether professional organizations exist, but whether their acceptance is mandatory.

The reason why this works in civil engineering is because the boss or the company cannot overrule the engineer. If the engineer declines to sign off some thingy as acceptable because X, Y and Z must be addressed, then that's it - the company can't proceed until the issues have been resolved; the management can't sign off by themselves, and they can't really even fire the engineer and get someone else to sign off for that because a complaint from the fired engineer about that would result in the process getting an independent review, (assuming the issues are real) the process getting stopped anyway, and the unethical engineer who agreed to sign off despite these flaws losing his/her licence - so that even if not signing gets you fired from one place, it's still the better choice than signing and being unable to ever work in that profession again. "Ethics standards in a profession" mean the standards that the profession imposes on its members even if they and their employer want to violate these standards.

Without effective enforcement, however, the whole process would be useless.

Of course, at least many of the mechanical engineers at auto companies most likely do have PEs. It's not just civil engineers. It's mostly any engineer/engineering manager who signs off on drawings, test, etc. for regulators. When I worked on oil rig designs, I started down the path to getting a PE and it would have been expected had I stayed in that business.

That said, I'm sure there would be lots of complaints if software had a similar system given that it would likely come with specific educational and other specific requirements.

Does all that happen often?

I don’t think it happens often.

Though Lawsuits are not uncommon in civil engineering. When I worked as an EIT (passed the state engineering exam, on way to becoming a Profesional engineer), our office did an analysis on someone else’s slope stability calculations, because the slope wasn’t stable and they wanted to figure out if it was done properly.

Civil engineering designs have a clear paper trail and the buck stops with the engineer who signed and stamped the drawings.

In many cases it is "you can over rule once", because that's all you're going to get. So no, it doesn't happen often, but the engineer legally has that power.