Perhaps a personality attribute like “fear of the unknown” the unknown in this case being magic. Basically magical xenophobia . At the most terrified end they hate the unknown and seek to destroy it, at the other end complete acceptance and even seeking it. Hating magic because magic is “scary” is a common fantasy trope.
There is a quote, which is a reversal of “High technology is indistinguishable from magic”, because if that is the case it must also be true that magic in a world with magic is effectively indistinguishable from technology (I forget who said that quote), but assuming toady rolls with this there will be worlds where magic is used like technology. (Another common trope) so it will be interesting to see what comes from this, I expect worlds with oppressive wizards aswell.
Magic isn't really as much the unknown in the fantasy world as it would be in our world. The more magic you have the less it becomes the unknown and the more it becomes
"scary things that other people can do". The other people part is crucial, if magic is something than anybody can do, just some people have more practice then that means that basically there is no clear distinct group to oppress, everybody is a little bit of a wizard. That kind of setup pretty much is what the Elder Scrolls, magic is not something that requires a special anything to use, the wizards are just folks that had more practice at it than you did.
Worlds with oppressed mages (look at you Dragon Age), needs wizards that are a distinct group, which threatens society with their powers but are not so powerful that the human race in general cannot feasibly defeat them. There we have the threat that they will suddenly decide to kill individuals on a whim, combined with the inability of them to kill the entire society of non-wizards without working up a sweat combines to result in society creating being able to create an organized body of non-wizards (templers in Dragon Age) to control and oppress wizards.
It's kind of odd to mention technology keeping pace with magic when there's a 15th century tech cutoff.
Nobody said that magic was necessarily more powerful than 15th century tech, between muskets and wizards, the muskets may well have the upper hand.
In any case, that is not my point. The point is that magic becomes technology whenever it is separable from the magic-user, so the +5 longsword in the hands of a D&D warrior is not really magic, even though it may have been originally created by magic it really functions as technology since it's use does not require magical powers. The same however does not apply to a wand of fireballs, even though it too is an enchanted object created by magic, it requires magical talent to actually use. This is where principle 5 is important here.
5. Magic must be separable from mundane technology, such that the latter can advance without reference to the former.
If muskets can beat wizards, this situation works fine for the muggles, until we get +5 muskets. Now the wizards win, because the wizards advance the technology so that they have the upper hand over the muggles, even if their own powers cannot direct contend with muskets in general, their ability to magically improve the muskets still gives them the edge.