Most places that offer "Free" storage, including Apple/iCloud, Dropbox, PhotoBucket, etc. would hope you need more than what they 'give' you free. You will then opt to
purchase more space. Simple. No hidden agenda. No different than "Buy two and get a third one free" ad or sale. I don't see any nefarious plans/purposes. YMMV. My only point was to present this as another choice.
It is twice what Apple offers with iCloud but does not provide any email service and other benefits of iCloud. Hardly a threat to Apple, that's for certain. I've had Dropbox almost from the beginning and still have gobs of space available. I simply don't use the space there or at iCloud for permanent backups. As I posted in another thread, we must be aware that things change, businesses close, 'free' space can disappear. "Don't put all your biscuits in the same oven." ... er, something like that!