> I believe Twitter, Youtube, Discord, Reddit, Imgur each had no monetization at all for the first 3~5 years of their existence

yes, their business plans was always to engage a lot of users losing VC money until you are a platform with enough moat to add monetization. It was the plan all along

It is the plan for plenty of startups: when it works you become a tech giant, otherwise you fail and no one knows you

Those are actually all pretty good examples of what I'm talking about, yeah. Investment money is not income, it is debt. It has to be paid back some time, or else your business will close. So the users who came to depend on the business will get boned when the business either closes or drastically changes as they find a business model.

OpenAI, for example, is not profitable as far as I know. I think the users they have now will be in for a rude awakening once they have to come up with a business model in order to pay back their investors. Startups that don't have a business model and get bought also regularly get shut down shortly later, leaving users stranded, look at Nest or Keybase for example off the top of my head.