Dropbox is extremely reliable, and has not given customers a real reason to switch imho. Evernote is famously unreliable with a "quirky" interface that often behaves strangely.
The pain of Evernote was enough to make me switch. Dropbox has not yet pained me enough to switch away from being a paying customer despite the fact that I have a 1GB OneDrive plan with Office.
I tried to switch away from paid 1TB Dropbox to the bundled ("free") 1TB OneDrive that's bundled with the Office subscription I need to have from time to time.
Filesystem integration with the Mac was disastrous. Three problems: 1- some characters are not permitted in filenames; you find this out when synch fails and have to guess where the problem is; 2 - some files simply silently don't synch; and 3 - a couple of times a day it would decide it had lost synch and then would have to re-index the repo, which not only took up cycles (I could survive that) but meant there was no synching while that was happening.
Whereas I just have almost everything in my DB directory tree and even do all my development there (builds and all).
At my last company we had Box which is almost identical with Dropbox but with a much more complex interface to satisfy corporate I/T. Total overkill for a startup!
The big difference between the two is that: Dropbox is the simplest version of any cloud storage concept that nearly every level of computer user can understand. Evernote is not simple.
Dropbox was an early solution, and put the effort in to make it nearly effortless to get set up.
They've also built a lot of good will from me over the years with promotional offerings. I don't actually pay for a subscription, but I've got about 13gb of quota.
I don't know why Dropbox is still about, and I don't know why Evernote is still about.
Dropbox seems to have found value in a flooded market although I don't know why, so it is conceivable that Evernote will do the same.