Do we have knowledge bases only because the logics are not automated enough?
Most logical systems in use are automated enough in principle. That is, there are algorithms which find the proof of a statement, if such a proof exists. The problem is computational complexity. Such algorithms are very, very, very, very, very slow. We only know efficient algorithms for special, easy cases.

More generally, knowledge representation is not just about logical deduction. You cannot logically deduce the fact that after Monday comes Tuesday and that tigers have legs, that is something that the machine has to be told, and it has to then store such knowledge. How do we store knowledge? That is a question of expressivity of the symbolic representation (the thing you call "logic"), and it is an issue that is largely separate logical deduction.