Google can't create a good spam filter, because enough users actually want to receive spam.
A machine can't distinguish between male enhancement pill spam and a newsletter recommending alex jones' supplements.
Or between "join our MLM today" and emails from recruiters.
Or between sales people sending cold emails and social engineering.
Google should ban both, but if they did, there'd be a huge outrage from idiots that actually want to receive content that's basically indistinguishable.
When pre-Musk Twitter tried to reduce the wave of fake news, they actually had to explicitly whitelist republican accounts because
> Most fake news on Twitter is spread by […] Republican, middle-aged White women residing in three conservative states, Arizona, Florida, and Texas
If GMail is getting worse, I can imagine that other, smaller mail services are getting much worse. The best explanation that I have read about why Google (and other major providers) are so good at spam filtering: They can observe a huge portion of the world's email, so they have the best training sets.
It is interesting that we never hear from GMail folks on HN. You see all kinds of Googlers pop-up into discussions with interesting insights about how the sausage is made. However, I cannot recall anyone from GMail appearing on HN to share some interesting behind-the-scenes stories.