I have several explanations:
No memory creation
I'd go as far as to say there is no canon spell to create memories. Yes, Hermione sent her parents away and made them believe they did not have a daughter - but this could potentially be accomplished with only (temporarily) removing memories.
Information vs Knowledge
A different explanation could be, that it would theoretically be possible to store some information in someones brain using a spell (or maybe potion), but that this would not mean that the person thus affected could also actively access that information.
In the real-world there have been experiments with teaching people in their sleep - which, as far as I can remember, basically just resulted in storing actual sentences/fragments in the sleeping persons mind without giving this person proper knowledge of their contents.
For example, if the person was taught "The Nile is the longest river in the world" that person would be able to repeat that fragment, but would be unable to answer the question "What is the longest river in the world?"
As far as I can tell almost any spell in the Potterverse has a limited duration, and the few spells that don't are mostly very rare, powerful and/or difficult to learn and cast (e.g. the forever burning branch which Hagrid offers as to the Giants a gift from Dumbledore ).
It could be that imprinting memories is possible, but using this trick as a learning highway is not feasible because the memories will fade after some time, leaving you with nothing.