They were seemingly everywhere and lots of apps and services offered Dropbox as an option. 200 million users in 2013.
Then they crippled the free plan and Apple and MS started pushing their services hard. And Dropbox seemed less ubiquitous after that.
I remember even Ubuntu had their own storage offering, which had they kept it going, I might have subscribed to to this day. Shame, would have been an easy way for Ubuntu to fund itself.