Well the same reason less than ethical webmasters use very near color CSS to hide text. They want or need the text there, but don’t really want you to see it. Webmasters however, are penalized for this deceptive technique, their rankings damaged and in turn their business damaged.
Recently, I have received some pretty tricky email marketing spamming emails. These emails, generally from a free account such as Yahoo seem innocent as they simply have the subject and content “test”. However, some have had a read receipt attached…. and even those that do not will receive bounces for those email addresses that are not valid.
If you haven’t read about the new “Brand Damaging” issues and you accept credit cards on your website… You need to. The potential impact on your business is too large to ignore.