Probably for the same reason I stopped: it's not fun. Given I have a finite amount of time to socialize my identity online, the value proposition of a service

Probably for the same reason I stopped: it's not fun. Given I have a finite amount of time to socialize my identity online, the value proposition of a service has to extend into emotion rather than pure pragmatism. Fun and joy: maximize this for me and my loyalty follows. If you want me to switch, you had best maximize these more than the existing player. In Googles case, the service just isn't fun. I always feel like I am missing things, it's hard to track comments you have read and the circle interface is klunky. Facebook has the same type of issues as an information service, but makes up for it in being a fun service for identity curation. Twitter is the best for a river-of-discourse type use case.