Which is the best selling point of Dropbox. It doesn't try to be an office app suite, a photo editing solution, a cloud collaboration platform, etc. It just syncs files between computers and phones, and has simple UX because of it.
Paying users? Why? Every user brings in 120 USD/Euro per year.
its limited to 2GB, but you could increase it by installing the app on your phone and enabling the auto upload of pictures. every picture increased it by (iirc) 5MB - and this extra space stayed if you removed the pictures.
haven't used it in ages though.
I know, I have used Dropbox since 2010 ;). But the free tier does not contribute to the revenue of Dropbox. There are no ads (except for Dropbox Pro/Business :p).
Dropbox has some deals with Samsung and others for coupons for certain phones, but most of the 1B is probably brought in by paid subscriptions. Since Dropbox costs $10 per month (plus some Packrat and Advanced Team users), there are roughly 8 million paying users who bring in the revenue. Since Dropbox has ~500 million users, that would be a conversion rate of 1.6%, which seems reasonable.
Of course, I could be way off.
The same can be said for the other software giants.
Also, for Dropbox to get to $1B in revenue they have hundreds of millions of users. This is a tremendous amount of adoption. Dropbox's real benefit lay in that it integrated directly into your OS so that it appeared just like a regular directory. This meant that usage patterns for users didn't change and so adoption ramped quicker.
Google on the other hand was always more of a work suite or productivity suite.
So ultimately what happened is that as the other large companies played catch up there simply wasn't enough of an advantage to switch to them away from Dropbox.