Why is this all happening? I'd argue that the reason is what I call the Law of Accelerated Intelligence:
As our amount of accumulated knowledge increases exponentially, the minimum amount of learning we need to do in order to productively participate or be a top performer in society increases. In other words, accelerated societal change necessitates accelerated intelligence.
Or as economist Ben Jones puts it, "If one is to stand on the shoulders of giants, one must first climb up their backs, and the greater the body of knowledge, the harder this climb becomes."
We've already felt this in our own daily lives too. When I first learned web design, all I needed to know was HTML and how to use Adobe Photoshop. Now, a web designer is expected to understand other languages too, understand how to do testing and analytics, and how to use a huge suite of other tools. And whether your career is web design, sales, journalism, or real estate, the digital world generated dozens of new skills to master.
For example, data science, programming, and artificial intelligence used to be niche skills. Now, having a basic understanding of them is more and more important for more and more professions. It's no longer enough to just get a degree or take a professional development course once a year. The learning needs to be constant.
Just like with running, being among the best gets more and more demanding with each passing year. Each generation of champions develops a body of best practices. The next generation must learn them and then build upon them, leaving those who come after them with even more to learn to get up to speed. And the cycle continues.