From a financial point of view it's probably more cost effective than paying some SEO outfit to carpet bomb the web with link spam. Of course the site itself must be fundamentally in a bad way if they are resorting to these measures of dragging visitors inside. Personally I would rather the money went to a charity of my choice and I get a receipt.
a: because I'm like that and ...
b: I'm cautious about who has my personal details & Paypal account number
Being purely mercenary if the money does not appear the site still gets a traffic boost from angry new members who will make it their mission in life to cause mayhem in there for months to come. Makes note to get the popcorn in for Sunday night