If you look at the demographics of US [1], you see that dip below the age of 30, so there are fewer folks coming online to take the jobs of the people retiring.
Of course there's immigration, various other methods to incentivize more people to join the IT sector, but ultimately it looks like there's fewer people to handle more work.
[0]: https://en.wikipedia.org/wiki/World_population see especially the projections in the side bar.
[1]: https://en.wikipedia.org/wiki/Demographics_of_the_United_Sta...