For me, the motivation for transparency came from too many frustrating instances of being kept in the dark after things had gone wrong. The worst thing both during and after an outage is poor communication, so I do my best to explain as much as I can what is going on during an incident and what's happened after one is resolved.

There's a very simple formula that I follow when writing a public port-mortem:

1. Apologize. You'd be surprised how many people don't do this , to their detriment. If you've harmed someone else because of downtime, the least you can do is apologize to them.

2. Demonstrate understanding of the events that took place.

3. Explain the remediation steps that you're going to take to help prevent further problems of the same type.

Just following those three very simple rules results in an incredibly effective public explanation.