Here is one - the alternative to ads everyone proposes is people pay for their content directly. Except there are catastrophic barriers to entry for such a business model:
* You need to bind real world money to online browsing, somehow. This means you need some kind of blunt "want to see the content? Pay X money, here are paypal and CC info links".
* People who do not have access to these tools - there is still a sizable chunk of America without a bank account, and often without access to credit cards - are thus cutoff from most web services.
* The Internet was predominantly built on principles of no barrier information exchange. Putting a paywall up is implicitly putting up a barrier to knowledge, which has deeper effects than just bottom lines on culture.
I would absolutely a lot of sites currently ignoring monetiziation and just using ads as a surrogate are making a mistake. I also recognize advertising is predatory and while I am arguing ads open up the Internet to the poor advertising also disproportionately harms the poor by manipulating them into making superfluous purchases they cannot afford.
But I also cannot condone a paywalled experience where you need to pay $3 to watch youtube, or $2 a month for Facebook, or $1 a month to use Twitter. Rent seeking is one of the great threats to civilization in our current era and the fundamental is that all these websites build value off of their exclusivity guaranteed by the state, thus making them the ultimate renteers of the services they offer because by definition nobody else can compete with them at being youtube or facebook or twitter - you can just make alternative products meant to fill the same niche. Its like using hand soap as a substitute for bar soap because someone owns the rights to physical bars of soap. It can do the same job but its not the same product.
Which is why I am extremely wary of pushing a paywalled Internet as a solution.
Now, there are absolutely alternatives to both models - Wikipedia demonstrates an annual fundraiser model akin to Kickstater or Patreon class crowdfunding to keep things running without ads or paywalls - but at the same time there are tons of comments about how Wikipedia should use ads so people don't have to feel guilty about not contributing when they don't have the money to do so while Wikimedia runs the large banner ads in December. Its the same psychological manipulation as ads, except possibly more benign since its from the project itself.
In a perfect world, all our software endeavors would be paid for before we even start writing them so that the code could be free and the servers run forever without worrying about money, but that model doesn't align with western shareholder-value driven markets at all. The whole point is to make something at fixed cost and extract potentially endless revenue from the monopoly IP gives you. For better or worse, that is how this economy is operating now.