Samsung used to be a very distant second behind Nokia in the smartphone market before Android came along, and there's no question Samsung wouldn't be the dominant player in the smartphone market that it is today, if it wasn't for Android to catapult it even beyond Apple in touchscreen smartphones, and beyond Nokia as a phone maker.
They've been benefiting from free development of Android from Google, when it could've cost them billions of dollars to get their own OS to the point where Android is today, and they've used the resources they saved by not doing that, and putting them into Tizen, to compete with Android. It should come as no surprise then that Google isn't very happy about this, then.
Right now Samsung says that Tizen is just a safety net, but in the same time, they are going to launch a Tizen device later this year that could have even better specs than the Galaxy S4 (due to it arriving months later), so I wouldn't put much faith into what Samsung says about it right now.
It's clear they want a strong alternative to Android, so they don't even need Microsoft's WP8 anymore to act as that alternative for them. They want their very own OS that they can build and customize however they want without anyone else being a major decision maker for it.
I still have very strong doubts that Tizen will be successful, and as I've mentioned before, no other modern mobile operating system has managed to "break through" the iOS and Android monopolies ever since they came out, and I very much doubt, Tizen, Bada's successor, is going to achieve that.
Google is most likely going to add a ton of new stuff to Android 5.0 this year, and whatever Tizen's goals are, they are most likely going to be easily surpassed by even the old versions of Android, let alone the new one. But the quality of the OS itself isn't even that important anymore, and it hasn't been for a while. What matters most by far is the ecosystem. Windows Phone has learned that the hard way, and Tizen is about to learn it, too, especially since unlike WP, Tizen is only going to be supported by one manufacturer alone. It's going to be very hard for it to become popular with both customers and carriers when only one company supports it, especially in today's market.