Not surprising. Apple's main business isn't building a file syncing service and while they're a much larger corporation I'd bet that Dropbox has more resources dedicated to its core product compared to Apple's iCloud file syncing offerings.
If Apple iCloud worked as well as Dropbox, I’d switch in a heartbeat.
I think the true reason you don't see too much fierce competition, is because of little profit you can make off of offering a raw storage, even with awesome client.
Even the almighty Dropbox alone may never be profitable...
https://qz.com/1214822/dropbox-is-filing-for-a-500-million-i...
But Dropox? Always works great. Always. Never had a problem. So I use them more and more. Too bad I can't encrypt my entire Dropbox like, say, Spideroak but oh well.
You might give gocryptfs [1] a try, with it you can keep [part of] your content encrypted in Dropbox.
Seriously. I am still surprised that to this day none of the big players can compete at Dropbox’s level. Not even Apple can make iCloud “Just Work™” the way Dropbox’s client apps and service work.
As a customer I use Dropbox because of how well it works, not because of its $/GB.