Liability. Professional engineers are liable for the work they produce and approve. They get a fancy stamp and liability insurance and can be sued when things go wrong. That's why engineers tend to be those who work on things that can kill you. IMO if you're working on an airplane's software for example you should probably either be an engineer or supervised by one. This matters because engineering provides you guidelines you must follow and ethics you must uphold, and if you aren't following the rules your governing professional body prescribes they can strip you of your license to prevent you from being a danger to the public. There are many other critical pieces of software btw. I just mentioned airplanes because it's one of the most obvious ones.

So yes, there definitely exist software engineers who require licensing by their state or country. Most of us just aren't actual software engineers, that's my point.