I get what you are saying, but the two cases are different. Typescript is a whole different language from Flow, so they can't interoperate. Every package that migrates to Typescript deprives the Flow ecosystem of compatibility and mindshare, so a win for one is always a loss for the other. Nobody wants to be a loser, so this will eventually resolve itself into a single dominant choice.

NPM and Yarn don't have this problem, since they are pretty much drop-in replacements for each other. As long as `yarn install` and `npm install` both get the job done equally well, picking one becomes a personal choice. Every project that adopts a standard package.json is a win for both NPM and Yarn. There doesn't need to be a loser in this case, and diversity is good.