ABs almost always show up if you browse Incognito. If you're signed into your account, you're more likely to see You May Also Like, which seems more weighted towards historical browsing patterns.
Apparently, Amazon doesn't realize I was checking the rank on that book because I was hate-stalking it. Jeez... don't be so oblivious, Amazon! Hate-stalking is normal reader behavior.
But really, the You May Also Like is going to be weighted towards that specific reader.
I think Amazon recs, in general, have trended towards the more popular (and Apub books). There used to be more recommendation love to go around. Now, it's more winner takes all. At least in my genres. I see more recommendations for hot popular book than book actually similar to book I just read, whether I'm reading a comp romance author or a non-fiction book.