Critique others' writing and walk on thin ice

I just read the first paragraph of one chapter of a book on legal writing. I had thumbed through the first few chapters until I found one whose topic interested me. That first paragraph seemed a bit dry and stuffy, so I paused to figure out why.

The paragraph had 8 sentences, and it had 8 passive-voice constructions in those 8 sentences. And that's being kind. It probably had 10--depending on how picky you want to be.

Now I ask you: is that good writing?

Even given the reality that passive-voice is not evil and that it has its uses, isn't an average of one per sentence a bit much? I think so.

Now, the thin-ice part (because maybe my own writing ain't so great): I encounter far too much mediocre writing in books and articles by legal-writing teachers.

Why?