Ask HN: How do Norton phishing scams get through Gmail spam filters?

I've been using gmail since the early beta days. One of the killer features was gmail's anti-spam capabilities.

In the last couple of months, I've noticed that phishing scams around renewing a Norton subscription keep getting routed to my inbox rather than spam folder. I've reported each of these as spam. I finally got around to just creating a "Norton" -> Spam filter. But I can't understand how gmail hasn't learned this after literally dozens of signals from me that all are extremely obvious as phishing mails from a human.

Is there something interesting going on in these mails that makes them so hard for gmail to get them right?