The thing about avoiding passive voice drives me batty- not just here, that admonition is everywhere. Sometimes it's useful, that's why it exists. Using it does not (necessarily) indicate a moral failing.
Generally speaking, I think it's because this advice is very easy to remember and repeat. Passive voice is easy to spot. Someone reading to look for errors can easily go "Aha! You did a naughty here." because they were once told that "passive = bad".
> "On religious tolerance, he gently referenced the Christians of Lebanon and Egypt, then lamented that the 'divisions between Sunni and Shia have led to tragic violence' (note the use of the passive voice)."
The only way that statement is in the "passive voice" is if you want to ding the speaker for not blaming someone specific; that is, it's only in the passive voice in the political sense. Grammatically, it's in the active voice.
Generally speaking, I think it's because this advice is very easy to remember and repeat. Passive voice is easy to spot. Someone reading to look for errors can easily go "Aha! You did a naughty here." because they were once told that "passive = bad".