Well, as per the most recent chapters, there has been a twist in that plot point. (⌒▽⌒)
I think in most of these stories, the setting is not that all nobles can use magic, but that all magic users became nobles, because they were stronger than the commoners.
Nobles tend to intermarry to keep their bloodlines thick, so most magic users are born into noble families and the few bastards born into commoner households probably never learned how to use magic on their own.
As CuddleQuill mentioned, there was a plot twist in the recent chapters, explaining why commoners in this story are not able to use magic, even if they are born with it.
There was one manga that made this concept make more sense then most tbh.
It wasn't that only nobles had magic but any commer that ended up having magic would be adopted into a noble house for marriage and strengthening the noble house more which cause the commoner class to have little/no magic users of their own to pass onto thr next generation
Isekai Yakkyoku (Isekai Pharmacy) has an aristocracy system that even nobles can end up being stripped of their rank if they somehow manage to lose their power.
Ooo!
I had forgotten about that one!!
ヾ(❀╹◡╹)ﾉ~
nobles have magic, commoners do not...
this story concept is prevalent in many magic fantasy stories, and everytime i find it dumb. i mean seriously people, each noble house has not existed since the dawn of time - obviously it had to become a noble house at some point. this means that once upon a time that house began as a commoner who had magic power...
i mean sure magic power is prob more likely to occur within same or similar bloodlines - who might currently be nobles - but the aristocracy is a manmade concept. magic power has always existed naturally in the world, but political power (and therefore nobility) is something made up by people at some point in the past.
i'm not just trashing on this story or anything, this is an idea i've seen in many other stories as well. it's just the idea that only nobles have magic power and commoners NEVER have it that bothers me and i find it annoying.