If you consider the set of all things to be learned. Some of those things will be easier to learn than others. Any intelligence setting itself to the task of

If you consider the set of all things to be learned. Some of those things will be easier to learn than others. Any intelligence setting itself to the task of learning things from this set is going to learn the easier things first. For a time, the power gained from learning early easy things may allow you to accelerate the rate of learning. But eventually you will hit a point where the things left to learn are so hard to learn, that the rate will start to decline. This does not imply something is wrong with our approach now, or wrong with people now. It is a natural and unavoidable thing, that the rate must at some point slow. Newtonian mechanics is incredibly simple to figure out, as evidenced by multiple people working it out about as soon as the tools were there to do so. General relatively quite a bit harder and more complex. Whatever rules tie the quantum world to general relatively appears to be trickier still. Hopefully we get there some day.