But it does seem like a double standard. Electricians can ask engineering questions, but not the other way around?
I'll answer your question with a question: Do you have a better idea?
I know that sounds kind of harsh, and I do not intend it that way. It's just that essentially, moderators have to come to some sort of consensus about what flies and what doesn't, and this is a fairly fair, easy to remember, easy to apply, safe standard.
I'm sure anyone with experience selling electrical services in the field has come across an "electrical engineer" of one stripe or another in their time that has done work in their own home that is at minimum not code compliant, and at worst a serious hazard. I think any of us on the forum that have been here for any length of time have seen borderline calls that slipped through, that we have to suspect that something is going to be done unsafe.
Conversely, I do not hear a whole lot of stories about electricians engineering their own work and it resulting in a hazard revealed later to an engineer.
In general, DIY electrical installation is something that is easier to spot, easier to stop and much more prevalent than people wandering in off the street just wanting to design their own installation. Even if DIY engineering caught on, I would like to think that these DIY engineers would hand their one-lines on cocktail napkins over to electricians to install, who would catch the engineering mistakes.