Yeah, it only takes a tiny percentage to respond, click on the link, download the file... whatever it is... and that is all they need because they send out so many million of these that a tiny percentage is still quite a lot of people.
People doing this are constantly trying to find ways of tricking the spam filters, then the spam filters catch up and the spammers find another way to trick them and it just keeps going and going and some get through and some are always successful