The model is not the issue, all of these make great profits. The issue is that companies don't just pursue making a profit they pursue making ALL the profit, ie growth. If growth does not exist then investment in a company is not very attractive and investors leave, lowering company value.
The problem is that they reach a growth saturation point, and when they have reached that point what they do is self-cannibalise by making their services worse in order to continue the "growth" (in total revenues). This continues to happen until they kill themselves by making the service so shitty the users leave.
It's a system that is not trying to make anything sustainable. Under capitalism everything is trying to pursue infinite growth and that inevitably results in this outcome.
Here is how platforms die: First, they are good to their users; then they abuse their users to make things better for their business customers; finally, they abuse those business customers to claw back all the value for themselves. Then, they die.
The issue is the system, this will not stop without changing to a system that places an emphasis on human development instead of infinite growth. These services should be developed to their saturation point and then upon reaching that point should be maintained at the highest quality they can support. This is the logical and most efficient outcome for people, and would put an emphasis on the sustainability of the infrastructure that is developed.
It is pure madness to do things this way. I'm convinced that if the workers owned these companies they would not cannibalise themselves, it's not the reddit staff that chose to do what reddit is doing, or the fandom staff, it's investors and the executives that perform their goals. If you purge them all what remains are people who usually genuinely care about the product, except for those dancing to the tune of the execs for some aspirational carrot being dangled in front of their nose.
Unfortunately, for most technology startups there are exactly two ways to pay salaries to the developers: getting investors (which lead to the exact cycle that I explained earlier) or paywalling the site up the wazoo (which leads to the community being necessarily smaller than it could have been otherwise).
Use a hybrid system. Market up until a service reaches a certain size then have government step in as the nationalising buyer to hand over ownership to the company's workers. A lot these services should be treated as utilities anyway, image hosting has gone through this cycle so many times I've lost count and imgur is on its way out too now. It's a fucking image host, it hosts images. That kind of shit should be a simple public service. It's a utility of the digital age. Don't get me started on Amazon reaching a very obvious inevitable saturation point that is based on the size of any given population and the average consumer goods range of a country.
Of course I know this can't work under capitalism, because the ideology of the capitalists will result in them intentionally fucking this up.
And even with no capitalism involved in the equation, how do we convince the government to get taxpayers to foot the bill for something as mundane as an image hosting service? Especially in an environment where even art and education are being severely restricted in cash flow due to them being "non-essential services"?
In terms of getting that through I really don't think it would be difficult, the main barrier is ideology as the actual usefulness of it is very obvious and it's easy to make the historic case that the private sector fails this industry over and over again. The biggest issue you would face is the one of whether porn should be allowed on it or not and I'd expect it to be a "not" outcome even in a socialist government. As for the costs point I don't see an issue, if they're profit-driven to begin with then they can run at break-even for government with the surplus either going to workers or going to improvement in quality of the services instead of to the investors.
Ideally I think a hybrid of private an national seems to work best, let the private sector build shit then take the important ones from them. At least while most of the world is still capitalist.
If ad companies would be paid according to customer conversion rate instead of how many ads they spam everywhere, it would collapse within a financial quarter.
Thinking that people support a brand or product that constantly annoys them is next-level stupid, but it's their main strategy. Google's conversion rate is less than 4% and instead of realizing that spamming trillions of ads on every site is causing that abysmal rate, they double down and get off to bigger "reach".
Also, Google lied to customers of their TrueView ads and just presented people muted autoplay ads instead. Here's an analysis about that.