The spammers monitor which web pages you are using and from that they figure out what your special needs and problems are. They send you email according to the marketing potential, where they think you are spending most of your money.
So for example, if you were browing web pages about pets, you would be getting a lot emails about selling to you pet food.
If you were browsing a lot of web pages about automobiles, you would be getting a lot of emails about selling to you cars, engine oil, windshield wiper fluid, and so on.
If you were browsing a lot web pages about stock market, you would be getting a lot of spam emails about investment advice, mutual funds, mortgages, and so on.
So most of your spam is about Viagra? Very interesting.