Also, the development and evolution of these open technologies relies on human interest and attention, and that attention can be diminished, even starved, by free, closed offerings.

Evil plan step 1: make a free closed alternative and make it better than everything else. Discord for chat, Facebook for forums and chat/email, etc.

Step 2: wait a few years, or a decade or more. The world will largely forget how to use the open alternatives. Instant messengers, forums, chat services, just give them a decade to die out. Privately hosted communities, either move to Facebook, pay for commercial anti-spam support, spend massive volunteer hours, or drown in spam.

Step 3: monetize your now-captive audience. What else are they going to use? Tools and apps from the 2000s?