Why Freshbooks not listed in the integrations?

Actually I don't even see Freshbooks listed in the integrations.

You are right. Freshbooks integration is not available at this moment. Though it was available earlier, it has been removed from the integrations due to changes in their API. 

I am forwarding the thread to our backend team as a feature request for evaluation. Unfortunately, we cannot provide any ETA at this moment. However, if there is any news you'll be updated here on this thread. 

Thanks!