Wages stopped increasing when human productivity peaked. The continued gains in productivity we have seen since that time have come by way of mechanization/automation. Given that the system encourages productivity, those who bring that automation to the economy reap the rewards. Those who only offer their labour to the economy are stuck since labour productivity has peaked. Humans simply cannot provide more productivity on their own.

As most people only offer labour and only a small group offer the more and more productivity gains of automation, it is true that the rewards end up being concentrated in that small group of productivity providing people. "The top" as you put it. That disparity is meant to incentivize you to develop your own technologies that increase productivity further instead of "wasting" your time selling productive-constrained labour, but in the real world it is unquestionably difficult to recognize where productivity can be gained.

The understanding of that was the basis for the idea behind pushing everyone into post-secondary schools, with a promise that higher learning would teach you how find solutions for increasing productivity, and thus increasing your reward for increasing overall productivity (a.k.a. providing you with a higher income). However, the real world is again messy and it hasn't really worked out. Despite a substantial increase in post-secondary attainment in recent times, the vast majority of graduates are making no more than they would have without having attended a post-secondary school (wages have been stagnant for decades upon decades) as they by and large end up only selling their productivity-limited labour.