Because software and the Internet are making it easier to provide more value, more quickly and more cheaply, than ever before. Thus, less jobs needed. Plus more of the jobs that are needed can be done off-shore, or, on-shore but with less office space and commuting, which in turn drives down money that needs to be spent on those sectors as well. Also the increasing popularity of so-called Agile and MVP philosophies is also driving down the cost of testing business ideas and getting to market. And yes, there's an increasing amount of actionable information, quality entertainment and useful functionality available for free on the Internet. So less money (needing to be) spent in those areas, thus less money available for jobs in those areas, for any given unit of product provided. Plus, due to the Internet, an increasing proportion of the revenue that comes into businesses (overall, but most proportionately in the software industries) can be captured by the owners/capitalists/entrepreneurs, rather than labor.

I'm not sure if this is a net win or net lose, overall, for the world. But it's certainly a net win for certain subsets of the population, and a net lose for other subsets. But even for those who it is a net lose, they are not forced to stay in some frozen static configuration or context, there are choices one can make to shift oneself to take better advantage of the new economic landscape, making it more likely to be a net win for them. It may not be easy. But few things in life are easy, and the universe doesn't guarantee anybody a free lunch (outside the more extreme cases of great inherited wealth, etc.)

One thing I'm sure of is that, all other things being equal, we're lucky to be in the field of software and the Internet at a time when this shift is occurring, because we're in a population subset where it can more easily be a net win for us.