Neither Reddit or Twitter are in any form shape or fashion a “monopoly”.
But, if you really want to look at the biggest companies in tech:
1. Apple was founded in 1977 and never racked up huge losses
2. Microsoft was profitable before it went public in 1980 and only took investor funding later on because BG wanted advice
3. Google never lost huge amounts of money
4. Facebook was profitable before going public and only went public because they had so many shareholders that they had the same reporting requirements as a public company.
5. Amazon (disclaimer my employer) is the only one that took huge losses early on.
So which “monopoly” do you believe operated at huge losses that is now successful?
And if you really want to be pedantic (not saying you are), Apple lost billions between 1995-1999. But not trying to capture market share. No one wanted their products.
Twitter and Reddit are just looking to get a share of the AI profits. Is it a monopolistic move? Maybe, I don't see where else the AI companies will be a able to get good structure data. The move is pointed towards the AI companies, specially new companies, not users. Since limiting user input will destroy the business model that sells data for AI companies. Going forward structured quality data will always have a price.
I expect for AI companies to buy twitter and/or reddit in the future so they aren't kept away from the data they need.
The alternate move is for AI companies to create their own products that they can use as a data pipe similar to twitter and reddit.
1 https://tedium.co/2023/06/21/reddit-api-free-rider-problem/
So what happens to them or their APIs is not important and they are not powerful in any real sense.
In comparison, Standard Oil was a real, powerful monopoly that controlled a key resource.
In the "tech world", I'd say Google is the one that matters because it has become the gatekeeper of the Web and Google ranking is critically important.
I wonder how long this will be true. Already today Googles search result are mostly SEO-optimized garbage and I can't fathom that this will get better now that "content creators" have access to plutonium grade bullshit generators.