I'd say there's an even more obvious reason than that; most content simply isn't valuable enough that people would pay for it. Can you support high quality journalism with a subscription model? Possibly, but the audience will be far lower than the audience on todays ad supported sites, and perhaps not even big enough to support two or three seperate ones.
Meanwhile, the vast majority of the world will simply look to any free source of news or information or whatever else that they can get.
And if everyone becomes part of a subscription model, it then leaves a gap in the market for whoever is willing to offer their services for free as a loss leader. As long as at least one person or organisation is willing to offer their services for free (even as part of a short term plan to get a large audience behind them), a subscription model will remain non viable for most sites and publications.
The core of the problem is that's easy and cheap to copy content(while rephrasing, for legality). So unless you need the content right now(or need it from a reliable source, say for your job/investments/etc), you could probably find most of what you're interested in offered for free, or something similar to it, which is good enough.
Meanwhile, the vast majority of the world will simply look to any free source of news or information or whatever else that they can get.
And if everyone becomes part of a subscription model, it then leaves a gap in the market for whoever is willing to offer their services for free as a loss leader. As long as at least one person or organisation is willing to offer their services for free (even as part of a short term plan to get a large audience behind them), a subscription model will remain non viable for most sites and publications.