I think this gets to the core of the problem. The API is out there and open, yet no one (or at least not many people) have decided to try and make a nice GUI client for Linux. Perhaps it's not a problem with Google but more a problem with publishing desktop/GUI software for Linux still being a complete pain in 2015. There's a fantastic talk from Dirk Hohndel last year about how much pain he's gone through creating and publishing a dive logging GUI application for Linux: https://www.youtube.com/watch?v=ON0A1dsQOV0 If someone like Dirk, who has access to no less than Linus Torvalds himself, has so much trouble creating a modern GUI app on Linux today then how much luck will anyone else have?
There's a startup called InSync [1] that produces a client that works on Linux, I've used it a couple of months back and it works.
But, trusting Google (or any company) with my data is a tough pill to swallow already, because I end up storing sensitive data, like for example I've got maybe one or two pictures of my naked wife, passwords of my accounts, backups of all emails I ever had and the list can continue. Trusting Google is one thing, but also trusting an obscure intermediary that asks for access to my data - no way. In writing this comment I couldn't even find out where they are located and this is the same story for most startups.
Also, in all fairness, if Google doesn't value me as a customer, then I'm voting with my wallet. A Linux user would have to be pretty dumb to pay Google money for Google Drive when alternatives like Dropbox exist. And to tell you the truth, I'm pretty tired of not being valued as a customer, even though I'm one of those people that pay up.
And I'm also an OS X user and frankly the OS X client sucks.