Spam evolved. The filters catch most of the egregious kind, but our mailboxes are still flooded with the rest: marketing of legitimate companies, which you likely interacted with at some point, however briefly, and often mixed into transactional messages. This consists the majority of most people's inbox; I bet it's the case for you too.

Depends on your provider. My GMail is fine, but my much older Hotmail is a spam cesspool. It's so bad I barely check it anymore the last couple of years, despite having been able to keep that email address since something like 1996. As I had "exposed" that to some email farms I probably got into some really bad spammers lists which Microsoft seems unable to stop.