Fabric fits in by providing twitter with a boat load of demographic and app usage data. They may still want that data for advertising purposes.

Having said that, I'm personally always wary about using an infrastructure piece for free. If my app relies on something, it's pretty important that it not easily go away. I can't count the HN threads of upset developers, frustrated about something being shuttered that was provided free.

Disclosure: I'm the co-founder of https://raygun.com which does mobile crash reporting, and more.