[tw04]

Because "email marketing" means "spammers". They were buying new blocks of IP addresses to try to evade blacklists. They are the scum of the internet, dumping their pollution far and wide because nobody is stopping them.

*to be clear, not all email marketers are spammers. But you can be damn sure anyone buying that many IP blocks is. There's literally no legitimate reason for them to need that many IP addresses.