I think that the problem for magazines is simple: cost of production. You have to sell a lot of advertising to break even, and then you also have to contend with a falling number of buyers of the product (the magazine).
But it's nothing new, and I think there's another factor has to be borne in mind: the demographics of the buying public. For example, when my wife was a teenager she used to buy perhaps two women's magazines every week. But, as she herself became wife and mother, she realised that the content of all of the magazines was much of a muchness - a cycle of seasonal fashion tips and cooking ideas, dating advice (?) and nonsense like that. She stopped buying. Now, with the dropping birth rate in some key constituencies, the natural market for this pap vanishes to the point where you need more and more prepaid ads and less dependency on kiosks and/or subscriptions, and smaller print runs mean higher unit costs, and a constant dumbing down to find more and more daft people to buy your crap...
And don't forget that paper itself now costs an arm and a leg, another factor that constantly drove my calendar market overheads the wrong way. Eventually, you find fewer and fewer clients who can dig deeply enough into their business pockets to take advantage of what you do. Was a time in the mid-70s that a small run of 3,000 units was doable; by the mid-80s that was a forgotten source of work, and you were looking for maybe 10,000 units to make it possible. So, those small clients had to resort to printers' offers of choosing from a number of standard formats and ready-made stock picture pages they held, with a cheap overprint of your company name.
The higher the basics cost, the greater the number of units you have to shift to stay accessible.
How the Internet ever makes any money from selling ads I don't know: I do all that I can to avoid having them on the monitor, and see them as an invasion of privacy. But then I see a lot of things in that light, so perhaps I'm not the typical punter that they seek.
Rob C