Dropbox isn't an OS storage, photo storage, mail storage, mobile devices backup all rolled into one (and all of that switched on by default) Comparing with Google Drive is fair, but the aforementioned stuff is why Google offers a fair 15Gb that you won't cap out soon.

I have almost 50Gb of free Dropbox storage btw, through referrals + events like the space race. But that's not really a fair fight anyway, since (aside from Dropbox) no one offers free space in exchange for actions..