Speaking only for yourself, of course. I know of several users (including myself) who have gone and registered giveaways after trying them on the site (even if months later). Often it might be the need to install on new computers, or to obtain updates with new features, improved performance, or squished bugs.
For many of the users "that will never buy it" - I'm guessing they have so many giveaways installed that for 90% of them "they will never use it" (long term)
For many people who download giveaways - most had probably never heard of the software before, would never have downloaded or used it, and would never have become a customer. Through participating with this site - even picking up 10 new customers, is probably 9 customers you would never have had.
Then there is the residual visibility of having a listing on this site - I've read more than once of somebody who finds this site for the first time (I don't know where they are all hiding, but there are more each day). They say, "I wish I found the site a week earlier - I really could've used XXXXXX". This shows the "giveaway" works for more than just 24 hours.
Forest and Trees?