Of course. Wizardry will likely become more common over time, but, not for a while. Even individuals with capacity (think about it like fluid intelligence) high enough to learn magic may not as a result of the scarcity of magical tomes and implements. I also like to stick, at least somewhat, to the idea that there are fewer wizards than there could be.
It is not just a representation of number, but also of skill.
Okay, so you've simply decided that the proliferation of wizardly magic hasn't accelerated
yet, not that it can't. That makes sense to me, since if there is a timeline of proliferation, a game or story has to be set
somewhere on that timeline. Greater socio-economic mobility, greater understanding of investment in social goods by rulers, greater access to information and transport, etc, will all create a logical point of acceleration for the development of any complex subject, but the effects will take time to be seen broadly.
Fair enough.
I have a question about the whole "idiosyncratic language" thing from upthread, though. In the 5e phb, at least, wizards can read another wizard's IL, translate it, and copy a spell in their own IL. This suggests that wizard magic is idiosyncratic because people are, not because magic is. Thus, it would make sense that one could, eventually, codify and systematize the learning of spells, especially those of low level.
So, one thing to wonder about, is who is trying to do this. Because the idea that no one is is wholly untenable. Someone, somewhere, is trying to be magic's Paracelsus, and may someday be credited as the grandparent of modern academic magic, or somesuch. ie, not all Alchemists actually tried to keep their findings secret, but instead tried to teach as many willing and able students as they could, review other alchemists works, and develop the sciences based on cross review and experimentation.