"which makes me wonder if they are desperate to sign up new customers."

For this kind of product, the 'one year free' strategy seems like a decent lure to me. If you use the service extensively, at the end of that year, you will have x GB of backups that you need to move elsewhere fast if you do not continue your subscription. That is way more of a hassle than, say, changing your Internet provider, phone company, or health insurance (at least in some parts of the world).

So, I guess their ploy is that users who cost them a lot during their free year will stay for years.