I'd be happy to use a first-party system designed for simply saying why I like something. However I'm not willing to create a Twitter account just so I can thank someone when we've never met (and likely never will), and are likely never to speak to each other again. Same deal with signing into other services through GitHub (like gitter), that might start sending me emails (when signing in via GitHub, the service gets your email address; so far as I know, gitter doesn't use it for anything, but other services might).
